Education  Library 


CONVERSATIONS 

ON 

CHEMISTRY ; 

IN  WHICH 

THE  ELEMENTS  OF  THAT  SCIENCE 

ARE 

FAMILIARLY  EXPLAINED 
AND 

ILLUSTRATED  BY  EXPERIMENTS, 

AND  SIXTEEN  COPPER-PLATE  ENGRAVINGS. 


•I" HE  EIGHTH  AMERICAN  FROM  THE  SIXTH   LONDON    EDITION,    RE 
VISED,  CORRECTED  AND  ENLARGED. 


TO  WHICH  ARE  NOW  ADDED, 

EXPLANATIONS  OP  THE  TEXT QUESTIONS  FOR  EXERCISE DI- 
RECTIONS FOR  SIMPLIFYING  THE  APPARATUS,  AND  A  VO- 
CABULARY OF  TERMS TOGETHER  WITH  A  LIST  OP 

INTERESTING  EXPERIMENTS. 

BY  DR.  J.  L.  COMSTOCK. 


HERTFORD: 

OLIVER  D.  COOKE. 

4822. 


c*^ 

DISTRICT  OF  CONNECTICUT,  M. 

BE  IT  REMEMBERED,  That  on  the  twenty  ninth  day 
L.  S.  of  December,  in  the  forty  sixth  year  of  the  Independence  of 
the  United  States  of  America,  Oliver  D.  Cooke  of  the  said 
District  hath  deposited  in  this  office  the  title  of  a  Book,  the  right 
whereof  he  claims  as  proprietor,  in  the  words  following;,  to  wit, 
"Conversations  on  Chemistry  :  in  which  the  elements  of  that  science 
are  familiarly  explained  arid  illustrated  by  experiments,  and  sixteen 
copperplate  engravings.  The  eighth  American  from  the  sixth  London 
edition,  revised,  corrected  and  enlarged.  To  which  are  now  added, 
explanations  of  the  text,  questions  for  exercise,  directions  for  simpli- 
fying the  apparatus,  and  a  vocabulary  ol  terms  ;  together  with  a  list  of 
interesting  experiments.  By  Dr.  J.  L.  Comstock."  In  conformity 
to  the  act  of  the  Congress  of  tbe  United  States,  entitled,  "  An  act  for 
the  encouragement  of  learning,  by  securing  the  copies  of  Maps,  Charts 
and  Books,  to  the  authors  and  proprietors  of  such  copies,  during  the 
times  therein  mentioned." 

CHAS.A.INGERSOLL, 
Clerk  of  the  District  of  Connecticut. 
A  true  copy  of  Record,  examined  and  sealed  by  me, 

CHAS.  A  INGERSOLL, 
Clerk  of  the  District  of  Connecticut. 


P.  B.  GOQDSE&L,  PRINTER. 


QD  * 
W3& 

ADVERTISEMENT 

l4itUC 

OF  THE  AMERICAN  EDITOR.       / 

THE  familiar  and  agreeable  manner  in  which  the  "  Conversations  on 
Chemistry"  are  written,  renders  this  one  of  the  most  popular  treatises 
on  the  subject  rvhich  has  ever  appeared.  The  elegant  and  easy  style 
also,  in  which  the  authoress  has  managed  to  convey  scientific  instruction 
is  peculiarly  adapted  to  the  object  of  the  work. 

In  some  respects,  however,  the  English  edition  may  be  considered  as 
objectionable.  A  book  designed  for  the  instruction  of  youth,  ought  if 
possible  to  contain  none  but  established  principles. 

Knowa  and  allowed  facts  are  always  of  much  higher  consequence 
than  theoretical  opinions.  To  youth,  particularly,  by  advancing  as 
truths,  doctrines  which  have  arisen  out  of  a  theory  not  founded  ou 
demonstration,  we  run  a  chance  of  inculcating  permanent  error. 

In  these  respects  we  think  that  iVIrs.  Bryan  has  not  been  sufficiently 
guarded.  The  brilliant  discoveries  of  Sir  Humphrey  Davy,  and  his 
known  eminence  as  a  Chemical  Philosopher,  seem  in  many  instances 
to  have  given  his  opinions  an  authority,  which,  in  the  mind  of  the  wri- 
ter, superseded  further  investigation.  Indeed  inferences  are  sometimes 
•JrawD  from  these  opinions  which  they  hardly  warrant.  Under  this 
view  of  the- subject,  a  part  of  the  notes  are  designed  to  guard  the  pupil 
against  adopting  opinions  which  he  will  find  either  contradicted,  or 
merely  examined  by  most  chemical  writers.  In  addition  to  this,  I 
fcave  made  such  explanations  of  the  text  as  I  thought  would  assist  the 
pupil  in  understanding  what  he  read. 

In  attempting  to  make  this  science  popular,  and  of  general  utility, 
it  is  of  great  importance  that  the  experiments  come  within  the  use  of 
such  instruments  as  are  easily  obtained.  I  have  therefore  given  such 
directions  on  thh  subject  as  my  former  experience,  as  a  lecturer, 
with  a  small  apparatus,  taught  me  to  believe  would  be  of  service. 

The  questions.  I  believe,  will  be  found  to  involve  whatever  is  most 
important  to  be  known  throughout  the  work. 

The  list  of  experiments  was  chiefly  made  up  without  referring  to 
books ;  some  few  of  them,  however,  are  copied  from  Parke,  Accum, 
£c. 

HARTFORD.  CT.  Jan.  1,  1822. 


M289981 


£N  venturing  to  offer  to  the  public,  and  more  particularly  to 
the  female  sex,  an  introduction  to  Chemistry,  the  author,  her- 
self a  woman,  conceives  that  some  explanation  may  be  required  ; 
and  she  feels  it  the  more  necessary  to  apologise  for  the  present 
undertaking,  as  her  knowledge  of  the  subject  is  but  recent,  and 
as  she  can  have  no  real  claims  to  the  title  of  chemist. 

On  attending  for  the  first  time  experimental  lectures,  the  au- 
thor found  it  almost  impossible  to  derive  any  clear  or  satisfacto- 
ry information  from  the  rapid  demonstrations  which  are  usual- 
ly, and  perhaps  necessarily,  crowded  into  popular  discourses  of 
this  kind.  But  frequent  opportunities  having  afterwards  oc- 
curred of  conversing  with  a  friend  on  the  subject  of  chemistry, 
and  of  repeating  a  variety  of  experiments,  she  became  better 
acquainted  with  the  principles  of  that  science,  and  began  to  feel 
highly  interested  in  its  pursuit.  It  was  then  that  she  perceiv- 
ed, in  attending  the  excellent  lectures  delivered  at  the  Royal 
Institution,  by  the  present  Professor  of  Chemistry,  the  great 
advantage  which  her  previous  knowledge  of  the  subject,  slight 
as  it  was,  gave  her  over  others  who  had  not  enjoyed  the  same 
means  of  private  instruction.  Every  fact  or  experiment  at- 
tracted her  attention,  and  served  to  explain  some  theory  to 
which  she  was  not  a  total  stranger  ;  and  she  had  the  gratifica- 
tion to  find  that  the  numerous  and  elegant  illustrations,  for 
which  that  school  is  so  much  distinguished,  seldom  failed  to 
produce  on  her  mind  the  effect  for  which  they  were  intended. 

Hence  it  was  natural  to  infer,  that  familiar  conversation  was; 
In  studies  of  this  kind,  a  most  useful  auxiliary  source  of  informa- 
tion ;  and  more  especially  to  the  female  sex,  whose  education  is 
seldom  calculated  to  prepare  their  minds  for  abstract  ideas,  or 
scientific  language. 

As,  however,  there  are  but  few  women  who  have  access  to 
this  mode  of  instruction  ;  and  as  the  author  was  not  acquainted 
with  any  book  that  could  prove  a  substitute  for  it,  she  thought 
that  it  might  be  useful  for  beginners,  as  well  as  satisfactory  to 
herself,  to  trace  the  steps  by  which  she  had  acquired  her  little 
stock  of  chemical  knowledge,  and  to  record,  in  the  form  of  dia- 
logues, those  ideas  which  she  had  first  derived  from  conversa- 
tion. 

But  to  do  this  with  sufficient  method,  and  to  fix  upon  a  mode 
of  arrangement,  was  an  object  of  some  difficulty.  After  much 
hesitation,  and  a  degree  of  embarrassment,  which,  probably,  the 
most  competent  chemical  writers  have  often  fell  in  common 
with  the  most  superficial,  a  mode  of  division  was  adopted, 
which,  though  the  most  natural,  does  not  always  admit  of  being 


PREFACE.  v. 

strictly  pursued— it  is  that  of  treating  first  of  the  simplest  bodies, 
and  then  gradually  rising  to  the  most  intricate  compounds. 

It  is  not  the  author's  intention  to  enter  into  a  minute  vindica- 
tion of  this  plan.  But  whatever  may  be  its  advantages  or  in- 
conveniences, the  method  adopted  in  this  work  is  such,  that  a 
young  pupil,  who  should  only  recur  to  it  occasionally  with  a 
view  to  procure  information  on  particular  subjects,  might  often 
find  it  obscure  or  unsatisfactory  ;  for  its  various  parts  are  so 
connected  with  each  other  as  to  form  an  uninterrupted  chain  of 
facts  and  reasonings,  which  will  appear  sufficiently  clear  and 
consistent  to  those  only  who  may  have  patience  tor  go  through 
the  whole  work,  or  have  previously  devoted  some  attention  to 
the  subject. 

It  will,  no  doubt,  be  observed,  that  in  the  course  of  these 
Conversations,  remarks  are  often  introduced,  which  appear 
much  too  acute  for  the  young  pupils,  by  whom  they  are  suppo- 
sed to  be  made.  Of  this  fault  the  author  is  fully  aware.  But, 
in  order  to  avoid  it,  it  would  have  been  necessary  either  to  omit 
a  variety  of  useful  illustrations,  or  to  submit  to  such  minute  ex- 
planations and  frequent  repetitions,  as  would  have  rendered  the 
work  tedious,  and  therefore  less  suited  to  its  intended  purpose. 

In  writing  these  pages,  the  author  was  more  than  once  check- 
ed in  her  progress  by  the  apprehension  that  such  an  attempt 
might  be  considered  by  some,  either  as  unsuited  to  the  ordinary 
pursuits  of  her  sex,  or  ill-justified  by  her  own  imperfect  know- 
ledge of  the  subject.  But,  on  the  one  hand,  she  felt  encouraged 
by  the  establishment  of  those  public  institutions,  open  to  both 
sexes,  for  the  dissemination  of  philosophical  knowledge,  which 
clearly  prove  that  the  general  opinion  no  longer  excludes  wo- 
men from  an  acquaintance  with  the  elements  of  science  ;  and, 
on  the  other,  she  flattered  herself,  that  whilst  the  impressions 
made  upon  her  mind,  by  the  wonders  of  Nature,  studied  in  this 
new  point  of  view,  were  still  fresh  and  strong,  trfie  might  per- 
haps succeed  the  better  in  communicating  to  others  the  senti- 
ments she  herself  experienced. 

The  reader  will  soon  perceive,  in  perusing  this  work,  that  he 
is  often  supposed  to  have  previously  acquired  some  slight  know- 
ledge of  natural  philosophy,  a  circumstance,  indeed,  which  ap- 
pears very  desirable.  The  author's  original  intention  was  to 
commence  this  work  by  a  small  tract,  explaining,  on  a  plan 
analogous  to  this,  the  most  essential  rudiments  of  that  science. 
This  idea  she  has  since  abandoned,  an  elementary  work  on 
Natural  Philosophy  having  appeared  just  as  the  first  edition  of 
the  "  Conversations  on  Chemistry"  was  preparing  for  the  press. 
Her  intended  tract,  however,  was  actually  written,  and  subsequent 
considerations  have  lately  induced  her  to  offer  it  to  the  public- 


CONTENTS. 

ON  SIMPLE  BODIES. 


CONVERSATION  I. 

Page 

ON  THE  GENERAL  PRINCIPLES  OF  CHEMISTRY.  i 

Connection  between  Chemistry  and  Natural  Philosophy. — Improved 
State  of  modern  Chemistry.— Its  Use  in  the  Arts. — The  general  ob- 
jects of  Chemistry. — Definition  of  Elementary  bodies.— Definition  of 
Decomposition.— Integrant  and  Constituent  Particles.— Distinction 
betvyeen  Simple  and  Compound  Bodies.— Classification  of  Simple 
Bodies. — Of  Chemical  Affinity,  or  Attraction  of  Composition. — Ex- 
amples of  Composition  and  Decomposition. 

CONVERSATION  II. 

CN  LIGHT  AND  HEAT.  14 

Light  and  heat  capable  of  being  separated. — Dr.  HerschcPs  Experi- 
msuts.  —  Phosphorescence. — Of  Caloric. — Its  two  .viodifications. — 
Free  Caloric. ...Of  the  three  different  States  of  Bodies,  solid,  fluid,  and 
aeriform. — Dilatation  of  s^lid  Bodies — Pyrometer — Dilatation  of 
Fluids. — Thermometer.— Dilatation  of  Elastic  Fluids. — Air  Ther- 
mometer.— Equal  Diffusion  of  Caloric. — Cold  a  Negative  Quality. 
— Professor  Prerosfs  Theory  of  the  Radiation  of  Heat.  —  Profes- 
sor Pictet's  Experiments  on  the  Reflection  of  Heat. — Mr.  Leslie's 
Experiments  on  the  Radiation  of  Heat. 

CONVERSATION  III. 

CONTINUATION    OF    THE    SUBJECT.  34 

Of  the  different  Power  of  Bodies  to  conduct  Heat. — Attempt  to  ac- 
count for  this  Power. — Count  Rumlord's Opinion  respecting  tho  non- 
conducting Po^  er  of  Fluids. — Phenomena  of  Boiling. — of  Solution 
in  general. —Solvent  Po-.ver  of  Water. —  Difference  between  Solu- 
tion and  iixture. — Solvent  power  of  Caloric. — Of  Clouds,  Rain, 
Dr.  Wells'  Theory  of  Dew,  Evaporation,  &c. — Influence  of  Atmos- 
pherical Pressure  on  evaporation. — Ignition. 

CONVERSATION  IV. 

•N  COMBINED  CALORIC,  COMPREHENDING  SPECIFIC   HEAT  AND  LA- 
TEST li-EAT.  57 

Of  Specific  Heat.— Of  the  different  Capacities  of  Bodies  for  Heat.— 
Specific  Heat  not  perceptible  by  the  Seoses. — How  to  be  ascertain- 


CONTENTS.  VII. 

eti. — Of  Latent  Heat. — Distinction  between  Latent  and  Specific 
Heat  — Phenomena  attending  the  Melting  of  Ice  and  the  Formation 
of  Vapour. — Phenomena  attending  the  Formation  of  Ice,  and  the 
Condensation  of  Elastic  Fluids  — Instances  of  Condensation,  and 
consequent  Disengagement  of  Heat,  produced  by  Mixtures,  by  the 
Slacking  of  Lime. — General  Remarks  on  Latent  Heat. — Explana- 
tion of  the  Phenomena  of  Ether  boiling,  and  Water  freezing,  at  tne 
same  i  emperature. — Of  the  Production  of  Cold  by  Evaporation. — 
Calorimeter. — Meteorological  Remarks 

CONVERSATION  V. 

OS  THE  CHEMICAL  AGENCIES  OF  ELECTRICITY.  74 

Of  Positive  and  Negative  Electricity. — Galvaui's  Discoveries. — Volta- 
ic Battery. — Electrical  Machine. — Theory  of  Voltaic  Excitement, 

CONVERSATION  VI. 

ON  OXYGEN-  AND  NITROGEN,  84 

The  Atmosphere  composed  of  Oxygen  and  Nitrogen  in  the  State  of 
Gas.— —Definition  of  Gas  — Distinction  between  Gas  and  Vapour. — • 
Oxygon  essential  to  Combustion  and  Respiration. — Decomposition 
of  the  Atmosphere  by  Combustion. — Nitrogen  Gaa  obtained  by  this 
Process  — Of  Oxygenation  in  grm-ial. — Ot  the  Oxydation  of  vletals. 
— Oxygen  Gas  obtained  from  Oxyd  of  vianganese.. — Description  of 
a  Water-Bath  for  collecting  and  preserving  Gases. — Combustion  of 
Iron  Wire  in  Oxygen  Gas. — Fixed  and  volatile  Products  of  Com- 
bustion.--Patent  Lamps. — Decomposition  of  the  Atmosphere  by 
Respiration. — Recomposition  of  the  Atmosphere. 

CONVERSATION  VII. 

ON   P YDROGEN.  98 

Of  Hydrogen. — Of  the  Formation  of  Water  by  the  Combustion  of 
Hydrogen. — Of  the  Decomposition  of  Water. — Detonation  of  Hy- 
drogen Gas. — Description  of  Lavoisier's  Apparatus  for  the  forma- 
tion of  Water. — Hydrogen  Gas  essential  to  the  Production  of  Flame. 
— Musical  Pone?  produced  by  the  Combustion  of  Hydrogen  Gas 
within  a  Glass  Tube.-— Combustion  of  Candles  explained.— -Gas 
lights. ---Detonation  of  Hydrogen  Gas  in  Soap  Bubbles --Air  Bal- 
loons.-- Meteorological  Phenomena  ascribed  to  Hydrogen  Gas. — 
Miner's  Lamp. 

CONVERSATION  VIII. 

ON  SULPHUR  AZVD  PHOSPHORUS.  116 

Natural  History  of  Sulphur  -—Sublimation.-— Alembic.— Combustion 
of  -ulphur  in  Atmospheric  Air  —Of  Acidification  in  general. — No- 
menclature of  the  Acids.—  Combustion  of  Sulphur  in  Oxygen  Gas, — 
Sulphuric  Acid. —Sulphurous  Acid. — Decomposition  of  s>ulphur.-~- 


VHI.  CONTENTS. 


-,     Phosphorus 

With    Sulphur.— Phosphorated   Hydrogen   Gas.-  Nomenclature    of 
Binary  Compounds. — Phosphcret  of  Lime  burning  under  Water. 

CONVERSATION  IX. 

Oft"     CARBON.  128 

Method  of  obtaining1  pure  Charcoal".— Method  of  making  common 
Charcoal.—  Pure -Carbon  not  to  he  obtained  by  Art.— Diamond. — 
Properties  of  Carbon. — Combustion  of  Carbon. — Production  of 
Carbonic  Acid  Gas.— Carbon  susceptible  of  only  one  Degree  of 
Acidification. — Gaseous  Oxyd  of  Carbon— Of  Seltzer  Water,  and 
other  Mineral  Waters.—  Effervescence, — Decomposition  of  Water 
by  Carbon.— Of  Fixed  and  Essential  Oils.— Of  the  Combustion  of 
Lamps  and  Candies.— Vegetable  Acids  —Of  the  Power  of  Carbon 
to  revive  Aietais. 

CONVERSATION   X. 

OJV     MKTALS.  141 

.Natural  History  of  Metals.— Of  Roasting,  Smelting,  &c.  Oxydation 
of  metals  by  the  Atmosphere. — Change  of  Colours  produced'  by  dif- 
ferent degrees  of  Oxyduriou. — Combustion  of  Metals. — Perfect  Met- 
als burnt  by  Electricity  only.-  Some  Metals  revived  by  Carbon  and 
other  Combustibles. — Perfect  Metals  revived  ly  Heat  alone.— Of 
the  Oxydation  of  certain  Metals  by  the  Decomposition  of  VVater. — 
Power  of  Acids  to  promote  this  Effect. — Oxydution  of  Metals  by 
Acids. — Metallic  Neutral  Salts. — Previous  oxyclaiion  of  the  Meta! 
requisite. — Ciystallisatioii. — Solution  distinguished  from  Dissolu- 
tion.— Five  metals  susceptible  of  acidification. — Meteoric  Stones. 
—Alloys,  Soldering,  Plating,  &c.-- Of  Arsenic,  and  of  the  caustic 
Effects  of  Oxygen.— Of  Verdigris,  Sympathetic  Ink,  &c.~ Of  the 
new  Metals  discovered  by  Sir  H.  Davy. 


ON  COMPOUND  BODIES. 

CONVERSATION  XIII. 

ON    THE    ATTRACTION    OF    COMPOSITION.  16J 

OF  the  Lawe  which  rrgulate  the  Phenomena  of  the  Attraction  of 
Composition.---!.  It  takes  place  only  between  Bodies  of  a  diflerent 
Nature.---^.  Between  the  most  minute  Particles  only.— 3.  Between 
2,  3,4,  or  more  rJodies.— Of  Compound  or  Neutral  Salts.— 4.  Pro- 
duces a  Change  of  Temperature— 5.  The  Properties  which  char- 
acterise Bodies  in  their  separate  State,  destroyed  by  Combination. 
'-6.  The  Force  of  Attraction  estimated  by  that  which  is  required" 


CONTENTS.  IX. 

•  >y  the  Separation  of  the  Constituents.— 7.  Bodies  have  amongst 
themselves  different  Degrees  of  Attraction. —Of  simple  elective 
and  double  elective  Attractions. — Of  quiescent  and  divellent  Forces. 
---Law  of  definite  Proportions.— -Decomposition  of  Salts  by  Volta- 
ic  Electricity. 

CONVERSATION  XIV. 

ON     ALKALIES.  173 

Of  the  Composition  and  general  properties  of  the  Alkalies. —Of  the 
new  discovered  Alkali  or  Lition.— Of  Potash.— Manner  of  pre- 
paring iu—Pearlash.— Soap.— -Carbonat  of  Potash.-— Chemical  No- 
menclature.---Solution  of  Potash.— Of  Glass.— Of  Nitrat  of  Pot- 
ash or  Saltpetre. —Effect  of  Alkalies  on  Vegetable  Colonrs.—  Of 
Soda.— Of  Ammonia  or  Volatile  Alkali  — Muriat  of  Ammonia.— - 
Ammoniacal  Gas. ---Composition  of  Ammonia.— Hartshorn  and  Sal 
Volatile.— Combustion  of  Ammoniacal  Gas. 

CONVERSATION    XV. 

ON     EARTHS.  183 

Composition  of  the  Earths.— Of  their  Incombustibility.— Form  the 
Basis  ol  all  Minerals.— Their  Alkaline  Properties,— Silex ;  its 
Properties  and  Uses  in  the  Arts.— Alumine  ;  its  Uses  in  Pottery, 
&c. — Alkaline  Earths. — Barytes. — Lime  ;  its  extensive  chemical 
Properties  and  Uses  in  the  Arts.— Magnesia.— Strontian. 

CONVERSATION   XVI. 

ON    ACIDS.  1#6 

Nomenclature  of  the  Acida.— Of  the  Classification  of  Acids.— 1st 
Class— Acids  of  simple  aim  known  Radicals,  or  Mineral  Acids.— 
~d  Class  — Acids  ot  double  Radicals,  or  Vegetable  Acids. — 3d  Ulass 
— Acids  of  triple  Radicals,  or  Animal  Acids. — Ol  the  Decomposi- 
tion, of  Acids  of  the  1st  Class  by  Combustible  Bodies. 

CONVERSATION  XVII. 

OJ?  THE  SULPHURIC  AND  PHOSPHORIC  ACIDS:  OR,  THE  COMBI- 
NATION'S OF  OXYGEN  VVITi,  SULPftUJR  AND  WITH  PHOSPHO- 
RUS, AND  OF  THE  SULPHATS  AND  PHOSPHATS.  201 

Of  the  Sulphuric  Acid. — Combustion  of  Animal  or  Vegetable  Bodies 
by  this  Ac  i*d. — .uethod  of  preparing  it. —  i  he  fculphurous  Acid  ob- 
tained in  the  Form  of  Ga?. —  /(ay  be  obtained  i'rorn  oulphuric  Ac- 
id.— May  be  reduced  to  i^uipijur — ,'s  absorbable  by  Water. — De- 
stroys Vegetable  Colours. — -)xyd  of  r'ulphur, — Of  Halts  in  general. 
— Sulphate. — SuJ^hat  of  Potash,  orSai  Poiychrest. — <>ld  produced 
by  the  malting  01  alts. —  ulphat  of  Soda,  or  «Jir»uher's  Salt. — 
Heat  evlvea  during  the  Formation  of  Salt*. — Crystallisation  of 
Salts. — Water  of  Crystallisation. — Efflorescence  and  Deliquescence 


X.  CONTENTS. 

of  Salts.— Sulphat  of  Lime,  Gypsum  or  Plaister  ©f  Paris. — Suiphat 

of  Magnesia. — Suiphat  of  Alumine,   or    Alum. — Suiphat  of  Iron. 

Of  Ink. — Of  the  Phosphoric  and   Phosphorous   Acids. — Phosphorus 
obtained  from  Bones. — Phosphat   of  Lime. 

CONVERSATION   XVIII. 

»F  THE  NITRIC  AND  CARBONAIC  ACIDS:  OR,  THE  COMBINATION 
OF  OXYGEN  WITH  NITROGEN  AND  WITH  CARBON  AND  OF  THE 
NITRATS  AND  CARBONATS.  209 

Nitrogen  susceptible  of  various  Degrees  of  Acidification. — Of  the 
Nitric  Acid. — Its  Nature  and  Composition  discovered  by  Mr.  Cav- 
endish— Obtained  from  Nitrat  of  Potash. — Aqua  Fortis. — Nitric 
Acid  may  be  converted  into  Nitrous  Acid. — Nitric  Ox  yd  Gas. — Its 
Conversion  into  Nitrous  Acid  Gas.  —  Used  as  an  Eudiometrical  Test. 
—Gaseous  Oxyd  of  Nitrogen,  or  exhilarating  Gas,  obtained  from 
Nitrat  of  Ammonia — Its  singular  Effects  on  being  respired. — Ni- 
trats.— Of  Nitrat  of  Potash,  Nitre  or  Saltpetre.— Of  Gunpowder. 
— Causes  of  Detonation. — Decomposition  of  Nitre. — Deflagration. 
— Nitrat  of  Ammonia. — Nitrat  of  Silver. — Of  the  Carbonic  Acid. 
— Formed  by  the  Combustron  of  Carbon. — Constitutes  a  component 
Part  of  the  Atmosphere. — Exhaled  in  some  Caverns. — Grotto  del 
Cane. — Great  Weight  of  this  Gas — Produced  from  calcareous 
Stones  by  Sulphuric  Acid. — Deleterious  Effects  of  this  Gag  when 
respired. — Sources  which  keep  up  a  Supply  of  this  Gas  in  the  At- 
mosphere.— Its  Effects  on  Vegetation. — Of  the  Carbonats  of  Lime  : 
Marble,  Chalk,  Shells,  Spars",  and  calcareous  Stones. 

CONVERSATION  XIX. 

®ff      THE    BORACIC,    FLUORIC,      MURIATIC,    AND    OXYGENATED    MU- 
RIATIC  ACIDS  ;      AND    ON    MURIATS.  223 

On  the  Boracic  Acid, — Its  Decomposition  by  Sir  H.  Davy. — Its  Basis 
Boracium. — Its  Recoroposition. — Its  Uses  in  the  Arts. — Borax  or 
Borat  of  Soda. — Of  the  Fluoric  Acid. — Obtained  from  Fluor  ;  cor- 
rodes Siliceous  Earth  ;  its  supposed  Composition. — Fluorine  ;  its 
supposed  Basis.— Of  the  Muriatic  Acid. — Obtained  from  Muriats. 
— Its  gaseous  Form. — Is  absorbable  by  Water. — Its  Decomposition. 
— I<«  susceptible  of  a  stronger  Degree  of  Oxygenation. — Oxygena- 
ted Muriatic  Acid. — Its  gaseous  Form  and  other  Properties. — Com- 
bustion of  Bodies  in  this  Gas. — It  dissolves  Gold- — Composition  of 
Aqua  Regia. — Oxygenated  Muriatic  Acid  destroys  all  O  lours  — - 
Sir  H.  Davy's  TheVryof  the  Nature  of  Muriatic  and  Oxymuriatic 
Arid. — Chlorine. — Used  for  Bleaching  and  for  Fumigation'?. — 1*9  of- 
fensive Smell,  &c. —  Muriate. —  Vluriat  of  Soda,  or  common  Salt. — 
Muriat  of  Ammonia.. ..Oxygenated  Muriat  of  Potash..  Detonates 
with  Sulphur,  Phosphorus,  Sic.  ...Experiment  of  burning  Phospho- 
rus under  Water  by  means  of  this  Salt  and  of  Sulphuric  Acid. 


CONTENTS.  XI. 

CONVERSATION  XX. 

ON  THE  NATURE  AND  COMPOSITION  OF  VEGETABLES.  236 

Of  organised  Bodies. — Of  the  Functions  of  Vegetables. — Of  the  ele- 
ments of  Vegetables. — Of  the  Materials  of  Vegetables. — Analysis  of 
Vegetables.— Of  Sap. — Mucilage,  or  Gum. — Sugar. — Manna,  and 
Honey. — Gluten. — Vegetable  Oils. — Fixed  Oils,  Linseed,  Nut,  and 
Olive' Oils. — Volatile  Oils,  forming  Essences  and  Perfumes. — Cam- 
phor.— Resins  and  Varnishes. — Pitch,  Tar,  Copal,  Mastic,  &c. — 
Gum  Resins Myrrh,  Assafoetida,  fcc. — Caoutchouc,  or  Gum  Elas- 
tic.— Extractive  colouring  Matter  ;  its  use  in  the  Arts  of  Dyeing  and 
Painting. — Tannin;  its  Use  in  the  Art  of  preparing  Leather. — 
Woody  Fibre. — Vegetable  Acids. — The  Alkalies  and  Salts  contain- 
ed ia  Vegetables. 

CONVERSATION  XXI. 

ON  THE  DECOMPOSITION  OF  VEGETABLES.  254 

Of  Fermentation  in  general. — Of  the  Saccharine  Fermentation,   the 

Product    of    which  is  sugar. Of  the  Vinous  Fermentation,   the 

Product  of  which  is  Wine.  Alcohol,  or  Spirit  of  Wine.  Analysis  of 
Wine  by  Distillation. — Of  Brandy,  Rum,  Arrack,  Gin,  &c. — Tar- 
trit  of  Potash,  or  Cream  of  Tartar. — Liqueurs. — Chemical  Proper- 
ties of  Alcohol. — Its  Combustion. — Of  Ether. — Of  the  Acetous  Fer- 
mentation, the  Product  of  which  is  Vinegar. — Fermentation  of  Bread. 
— Of  the  Putrid  Fermentation,  which  reduces  Vegetables  to  their 
Elements. — Spontaneous  Succession  of  these  Fermentations. — Of 
Vegetables  said  to  be  petrified. — Of  Bitumens:  Naphtha.  Asphal- 
tum,  Jet,  Coal,  Succin,  or  Yellow  Amber. — Of  Fossil  Wood,  Peat, 
and  Turf. 

CONVERSATION  XXII- 

HISTORY    OP  VEGETATlONi  272 

Connection  between  the  Vegetable  and  Animal  Kingdoms. — Of  Ma- 
nures.— Of  Agriculture. — Inexhaustible  Sources  of  Materials  for  the 
Purposes  of  Agriculture. — Of  sowing  Seed. — Germination  of  ths 
Seed. — Function  of  the  Leaves  of  Plants. — Effects  of  Light  and  Air 
on  Vegetation. — Effects  of  Water  on  Vegetation  — Effects  of  Vegeta- 
tion on  the  Atmosphere.-r-Formation  of  Vegetable  Materials  by  the 
Organs  of  Plants, — Vegetable  Heat. — Of  the  Organs  of  Plants. — Of 
the  Bark,  consisting  of  Epidermis,  Parenchyma,  and  Cortical  Lay- 
ers.— Of  Alburnum,  or  Wood. — Leaves,  Flowers,  and  Seeds. — Effects 
of  the  Season  on  Vegetation. — Vegetation  of  Evergreens  in  Winter. 

CONVERSATION  XXIII. 

»N   THE    COMPOSITION   OF   ANIMALS.  288 

Eieaaenfs  «f  animals.— Of  the  principal  Materials  of  Animals,  viz.  GeJ- 
atine,  Albumen,  Fibrine,  Mucus. — Of  Animal  Acids. — Of  Animal  C«- 
tewrs,  Prussian  Blue,  Caraaine,  and  Ivory  Black. 


XJi.  CONTENTS. 

CONVERSATION  XXIV 

ON    THE    ANIMAL    ECONOMY.  297. 

Of  the  principal  Animal  Organs. — Of  Bones,  Teeth,  Horns,  Ligaments, 
and  Cartilage. — Of  the  Muscles,  constituting  the  Organs  of  Motion. 
...Of  the  Vascular  System,  for  the  Conveyance  of  I  luiris. — Ol  the 
Glands,  for  the  ^ecr-.-tion  of  Fluids. — Of  the  Nerves,  constituting  the 
Organs  of  Sensation. — Of  the  Cellular  Substance  which  connects  the 
several  Organs. — Of  the  Skin. 

CONVERSATION  XXV. 

OK   ANIMALISATION,  NUTRITION,  AND  RESPIRATION.  3Q5 

Digestion. — Solvent  Power  of  the  Gastric  Juice. — Formation  of  a 
Chyle. — Its  Assimilation,  or  Conversion  into  Blood. — Of  Respira- 
tion.— Mechanical  Process  of  ttespiration. — Chemical  Process  of 

Respiration Of  the  Circulation   of  the  Blood. — Of  the  Functions 

of  the  Arteries,   the  Veins,  and  the  Heart. — Of  the  Lungs. — Effects 
of  Respiration  on  the  Blood. 

CONVERSATION   XXVI. 

ON  ANIMAL  HEAT  ;    AND    OP   VARIOUS    ANIMAL  PRODUCTS.  315 

Of  the  Analogy  of  Combustion  and  Respiration. — Animal  Heat  evolv- 
ed in  the  Lungs — Animal  Heat  evolved  in  the  Circulation. — Heat 
produced  by  Fever. — Perspiration. — Heat  produced  by  Exercise—- 
Equal  Temperature  of  Animals  at  all  Seasons. — Power  of  the  Animal 
Body  to  resist  the  Effects  of  Heat. — Cold  produced  by  Perspiration. 
— Respiration  of  Fish  and  of  Birds. — Effects  of  Respiration  on  Mus- 
cular Strength. — Of  several  Animal  Products,  viz.  Milk,  Butter,  and 
Cheese;  Spermaceti;  Ambergris;  Wax;  Lac;  Silk;  Musk;  Ci 
ret;  Castor.-— Of  the  putrid  Fermentation. — Conclusion. 


CONVERSATIONS 

ON 

CHEMISTRY. 

CONVERSATION  I. 

ON  THE  GENERAL  PIUNCIPLES  OF  CHEMISTRY. 


Mrs.  B.  As  you  have  now  acquired  some  elementary  no- 
tions of  NATURAL  PHILOSOPHY,  1  am  going  to  propose  to  you 
another  branch  of  science  to  whicri  1  am  particularly  anxious 
that  you  should  devote  a  share  of  your  attention.  This  is 
CHEMISTRY,  which  is  so  closely  connected  with  Natural  Philos- 
ophy, that  the  study  of  the  one  must  be  incomplete  without 
some  knowledge  of  the  other  ;  for,  it  is  obvious  that  we  can  de- 
rive but  a  very  imperfect  idea  of  bodies  from  the  study  of  the 
general  laws  by  which  they  are  governed,  if  we  remain  totally 
ignorant  of  their  intimate  nature. 

Caroline.  To  confess  the  truth,  Mrs.  B.,  I  am  not  disposed 
to  form  a  very  favourable  idea  of  chemistry,  nor  do  1  expect  to 
derive  much  entertainment  from  it.  1  prefer  the  sciences  which 
exhibit  nature  on  a  grand  scale,  to  those  that  are  confined  to 
the  minutiae  of  petty  details.  Can  the  studies  which  we  have 
lately  pursued,  the  general  properties  of  matter,  or  the  revolu- 
tions of  the  heavenly  bodies,  be  compared  to  the  mixing  up  of 
a  few  insignificant  drugs  ?  I  grant,  however,  there  may  be  en- 
tertaining experiments  in  chemistry,  and  should  not  dislike  to 
try  some  of  them  :  the  distilling,  for  instance,  of  lavender,  or 
rose  water 

Mrs.  B.  I  rather  imagine,  my  dear  Caroline,  tnat  your  want 
of  taste  for  chemistry  proceeds  from  the  very  limited  idea  you 
entertain  of  its  object.  You  confine  the  chemist's  laboratory 
to  the  narrow  precincts  of  the  apothecary's  and  perfumer's 
shops,  whilst  >it  is  subservient  to  an  immense  variety  of  other 
useful  purposes.  Besides,  my  dear,  chemistry  is  by  no  means 
confined  to  works  of  art.  Nature  also  has  her  laboratory^ 

VOL.  i.  ! 


24  GENERAL,    PRINCIPLES 

which  is  the  universe,  and  there  she  is  incessantly  employed  in 
chemical  operations.  You  are  surprised,  Caroline  ;  but  i  as- 
sure you  that  the  most  wonderful  and  the  most  interesting  phe- 
nomena of  nature  are  almost  all  ot  them  produced  by  chemic- 
al powers.  What  Bergman,  in  the  introduction  to  his  history 
of  chemistry,  has  said  of  this  science,  will  give  you  a  more  just 
and  enlarged  idea  of  it.  The  knowledge  of  nature  may  be 
divided,  he  observes,  into  three  periods.  The  first  is  that  in 
which  the  attention  of  men  is  occupied  in  learning  the  external 
forms  and  characters  of  objects,  and  this  is  called  Natural  His- 
tory. In  the  second,  they  consider  the  effects  of  bodies  acting 
on  each  other  by  their  mechanical  power,  as  their  weight  and 
motion,  and  this  constitutes  the  science  of  Natural  Philosophy. 
The  third  period  is  that  in  which  the  properties  and  mutual  ac- 
tion of  the  elementary  parts  of  bodies  are  investigated.  This 
last  is  the  science  of  CHEMISTRY,  and  I  have  no  doubt  you  will 
soon  agree  with  me  in  thinking  it  the  most  interesting. 

\ou  may  easily  conceive,  therefore,  that  without  entering  in- 
to the  minute  details  of  practical  chemistry,  a  woman  may  ob- 
tain such  a  knowledge  of  the  science  as  will  not  only  throw  an 
interest  on  the  common  occurrences  of  life,  but  will  enlarge  the 
sphere  of  her  ideas,  and  render  the  contemplation  of  nature  a 
scene  of  delightful  instruction. 

Caroline.  If  this  is  the  case,  I  have  certainly  been  much  mis- 
taken in  the  notion  1  had  formed  of  chemistry.  I  own  that  I 
thought  it  was  chiefly  confined  to  the  knowledge  and  prepara- 
tion of  medicines. 

Mrs.  B.  That  is  only  a  branch  of  chemistry  which  is  called 
Pharmacy;  and  though  the  study  of  it  is,  no' doubt,  of  great 
importance  to  the  world  at  large,  it  bt longs  exclusively  to  pro- 
fessional men,  and  is  therefore  the  last  that  I  should  advise  you 
to  pursue. 

Emily.  But,  did  not  the  chemists  formerly  employ  them- 
selves in  search  of  the  philosopher's  stone,  or  the  secret  of 
making  gold  ?* 

*The  Alchymists  had  in  view  three  great  objects  of  discovery,  viz. 
1st.  The  Elixir  of  health;  by  the  use  of  which  the  lives  of  men  mignt 
be  protracted  to  any  desirable  length,  or  their  mortality  prevented. 
'2nd.  The  universal  solvent,  or  a  liquid  which  should  dissolve  every 
other  substance  This  it  was  supposed  would  lead  to  the  grand  dis- 
covery, viz.  3rd.  The  making  of  gold,  or  finding  the  philosophers  slone. 
That  men  of  sound  and  discriminating  minds  on  other  subjects,  should 
imve  spent  their  whole  lives  in  pursuits  so  chimerical,  is  to  us  wonder- 
ful indeed.  But  our  wonder  ceases  in  some  degree,  when  we  are  told 
that  the  doctrine  of  transmutation,  kc.  wns  founded  on  a  Theory, 
•which,  in  the  12th  century,  was  considered  as  plausible,  as  we  coosid- 


OP    CHEMISTRY.  o 

Mrs.  B.  These  were  a  particular  set  of  misguftled  philoso- 
phers, who  dignified  themselves  -with  the  name  of  \lchemists, 
to  distinguish  their  pursuits  from  those  of  the  common  chemists, 
whose  studies  were  confined  to  the  knowledge  of  medicines. 

But  since  that  period,  chemistry  has  undergone  so  complete 
a  revolution,  that,  from  an  obscure  and  mysterious  art,  it  is  now 
become  a  regular  and  beautiful  science,  to  which  art  is  entirely 
subservient.  Tt  is  true,  however,  that  we  are  indebted  to  the 
alchemists  for  many  very  useful  discoveries,  which  sprung 
from  their  fruitless  attempts  to  make  gold,  and  which,  undoubt- 
edly} have  proved  of  infinitely  greater  advantage  to  mankind 
than  all  their  chimerical  pursuits. 

The  modern  chemists,  instead  of  directing  their  ambition  to 
the  vain  attempt  of  producing  any  of  the  original  substances  in 
nature,  rather  aim  at  analyzing  and  imitating  her  operations, 
and  have  sometimes  succeeded  in  forming  combinations,  or  ef- 
fecting decompositions,  no  instances  of  which  occur  in  the 
chemistry  of  Nature.  They  have  little  reason  to  regret  their 
inability  to  make  gold,  whilst,  by  their  innumerable  inventions 
and  discoveries,  they  have  so  greatly  stimulated  industry  and 
facilitated  labour,  as  prodigiously  to  increase  the  luxuries  as 
well  as  the  necessaries  of  life. 

Emily.  But  I  do  not  understand  by  what  means  chemistry 
can  facilitate  labour;  is  not  that  rather  the  province  of  the  me- 
chanic ? 

Mrs.  B.  There  are  many  ways  by  which  labour  may  be 
rendered  more  easy,  independently  of  mechanics ;  but  mechan- 
ical inventions  themselves  often  derive  their  utility  from  a  chem- 
ical principle.  Thus  that  most  wonderful  of  all  machines,  the 
Steam-engine,  could  never  have  been  invented  without  the  as- 
sistance of  chemistry.  In  agriculture,  a  chemical  knowledge  of 
the  nature  of  soils,  and  of  vegetation,  is  highly  useful  ;  and.  in 
those  arts  which  relate  to  the  comforts  and  conveniences  of  life, 
it  would  be  endless  to  enumerate  the  advantages  which  result 
from  the  study  of  this  science. 

er  many  of  ours  at.  the  present  day,  viz.  T^hat  a  perfect  metal'consist- 
ed  nf  quicksilcer  and  sulphur;  these,  when  pure  and  united,  formed 
gold.  Tha.  a:l  oth-.-r  m  -tais  contained  a  quantity  of  dross,  which 
pr  v  nt.ed  the  particles  of  these  two  substances  from  uniting.  If 
therefore,  this  dross  could  he  got  rid  of  in  the  other  metals,  gold  would 
be  the  result.  They  believed  also,  that  nature  herself  favoured  this 
operation.  Thus  Friar  lloger  Bacon,  in  his  Mirror  of  Alchymy,  say?, 
"I  must  tell  you,  that  nature  ahvaies  inlendeth  and  striueth  to  the  per- 
fection of  gold  ;  hut  many  accidents  comraing  between,  change  the  met- 
fcc  "  S-e  his  Book  printed  in  1697,  Chap.  ii.  C. 


4  GENERAL   PRINCIPLES 

Caroline.  But  pray,  tell  us  more  precisely  in  what  manner 
the  discoveries  of  chemists  have  proved  so  beneficial  to  so- 
eiety  ? 

Mrs.  B.  That  would  be  an  injudicious  anticipation  ;  for 
you  would  not  comprehend  the  nature  of  such  discoveries  and 
useful  applications,  as  well  as  you  will  do  hereafter.  Without 
a  due  regard  to  method,  we  cannot  expect  to  make  any  pro- 
gress in  chemistry.  I  wish  to  direct  your  observations  chiefly 
to  the  chemical  operations  of  Nature  ;  but  those  of  Art  are  cer- 
tainly of  too  high  importance  to  pass  unnoticed.  We  shall 
therefore  allow  them  also  some  share  of  our  attention. 

Emily.  Well,  then,  let  us  now  set  to  work  regularly.  I  am 
very  anxious  to  begin. 

Mrs.  B.  The  object  of  chemistry  is  to  obtain  a  knowledge  of 
the  intimate  nature  of  bodies,  and  of  their  mutual  action  on 
each  other.  You  find  therefore,  Caroline,  that  this  is  no  nar- 
row or  confined  science,  which  comprehends  every  thing  mate- 
rial within  our  sphere. 

Caroline.  On  the  contrary,  it  must  be  inexhaustible ;  and 
I  am  at  a  loss  to  conceive  how  any  proficiency  can  be  made  in 
a  science  whose  objects  are  so  numerous. 

Mrs.  B.  If  every  individual  substance  were  formed  of  differ- 
ent materials,  the  study  of  chemistry  would,  indeed,  be  endless  ; 
but  you  must  observe  that  the  various  bodies  in  nature  are  com- 
posed of  certain  elementary  principles,  which  are  not  very  nu- 
merous. 

Caroline.  Yes  ;  I  know  that  all  bodies  are  composed  of  fire, 
air,  earth,  and  water;  I  learnt  that  many  years  ago. 

Mrs.  B.  But  you  must  now  endeavour  to  forget  it.  I  have 
already  informed  you  what  a  great  change  chemistry  has  under- 
gone since  it  has  become  a  regular  science.  Within  these  thir- 
ty years  especially,  it  has  experienced  an  entire  revolution,  and 
it  is  now  proved,  that  neither  fire,  air,  earth,  nor  water,  can  be 
called  elementary  bodies.  For  an  elementary  body  is  one  that 
has  never  been  decomposed,  that  is  to  say,  separated  into  oth- 
er substances  ;  and  fiiv,  air,  earth,  and  water,  are  all  of  them 
susceptible  of  decomposition. 

Emily.  I  thought  that  decomposing  a  body  was  dividing  it 
into  its  minutest  parts.  And  if  so,  I  do  not  understand  why  an 
elementary  substance  is  not  capable  of  being  decomposed,  a,s 
well  as  any  other. 

Mrs.  B.  You  have  misconceived  the  idea  of  decomposition  ; 
it  is  very  different  from  mere  division.  The  latter  simply  re- 
duces a  body  into  parts,  but  the  former  separates  it  into  the  va- 
rious ingredients,  or  materials,  of  which  it  is  composed.  If  we- 


OF   CHEMISTRY. 

to  take  a  loaf  of  bread,  and  separate  the  several  ingredi* 
ents  of  which  it  is  made,  the -flour,  the  yeast,  the  salt,  and  the 
water,  it  would  be  very  different  from  cutting  or  crumbling  the 
loaf  into  pieces. 

Emily.  I  understand  you  now  very  well.  To  decompose  a 
body  is  to  separate  from  each  other  the  various  elementary  sub- 
stances of  which  it  consists. 

Caroline.  But  flour,  water,  and  other  materials  of  bread,  ac- 
cording to  your  definition,  are  not  elementary  substances. 

Mrs.  B.  JNo,  my  dear  ;  I  mentioned  bread  rather  as  a  famil- 
iar comparison,  to  illustrate  the  idea,  than  as  an  example. 

The  elementary  substances  of  which  a  body  is  composed  are 
called  the  constituent  parts  of  that  body  ;  in  decomposing  it, 
therefore,  we  separate  its  constituent  parts.  If,  on  the  contra- 
ry, we  divide  a  body  by  chopping  it  to  pieces,  or  even  by  grind- 
ing or  pounding  it  to  the  finest  powder,  each  of  these  small  par- 
ticles will  still  consist  of  a  portion  of  the  several  constituent 
parts  of  the  whole  body:  these  are  called  the  integrant  parts  j 
do  you  understand  the  difference  ? 

Emily.  Yes,  I  think,  perfectly.  We  decompose  a  body  in- 
to its  constituent  parts  ;  and  divide  it  into  its  integrant  parts. 

Mrs  B.  Exactly  so.  If  therefore  a  body  consists  of  only 
one  kind  of  substance,  though  it  may  be  divided  into  its  inte- 
grant parts,  it  is  not  possible  to  decompose  it.  Such  bodies  are 
therefore  called  simple  or  elementary,  as  they  are  the  elements 
of  which  all  other  bodies  are  composed.  Compound  bodies  are 
such  as  consist  of  more  than  one  of  these  elementary  principles. 

Caroline.  But  do  not  fire,  air,  earth,  and  water,  consist,  each 
of  th«3m,  but  of  one  kind  of  substance  ? 

Mrs.  B.  No,  my  dear  ;  they  are  every  one  of  them  sucepti- 
ble  of  being  separated  into  various  simple  bodies.  Instead  of 
four,  chemists  now  reckon  upwards  of  forty  elementary  substan- 
ces. The  existence  of  most  of  these  is  established  by  the  clear- 
est experiments  ;  but,  in  regard  to  a  few  of  them,  particularly 
the  most  subtle  agents  of  nature ;  heat,  light,  and  electricity , 
there  is  yet  much  uncertainty,  and  I  can  only  give  you  the  opin- 
ion which  seems  most  probably  deduced  from  the  latest  discov- 
eries. After  I  have  given  you  a  list  of  the  elementary  bodies, 
classed  according  to  their  properties,  we  shall  proceed  to  exam- 
ine each  of  them  separately,  and  then  consider  them  in  their 
combinations  with  each  other. 

Excepting  the  more  general  agents  of  nature,  heat,  light,  and 
2* 


%  GENERAL   PRINCIPLES 

electricity,  it  would  seem  that  the  simple  form  of  bodies  is  that 
of  a  metal.* 

Caroline.  You  astonish  me  !  I  thought  the  metals  were  only 
one  class  of  minerals,  and  that  there  were  besides,  earths, 
stones,  rocks,  acids,  alkalies,  vapours,  fluids,  and  the  whole  of 
the  animal  and  vegetable  kingdoms. 

Mrs.  B.  You  have  made  a  tolerably  good  enumeration^ 
though  I  fear  not  arranged  in  the  most  scientific  order.  All 
these  bodies,  however,  it  is  now  strongly  believed,  may  be 
\iltimately  resolved  into  metallic  substances.!  Your  surprise 
at  this  circumstance  is  not  singular,  as  the  decomposition  of 
some  of  them,  which  has  been  but  lately  accomplished,  has  exci- 
ted the  wonder  of  the  whole  philosophical  world. 

But  to  return  to  the  list  of  simple  bodies — these  being  usually 
found  in  combination  with  oxygen,  I  shall  class  them  according 
to  their  properties  when  so  combined.  This  will,  I  think$  fa- 
cilitate their  future  investigation. 

Emily.  Pray  what  is  oxygen  ? 

Mrs.  B.  A  simple  body  ;  at  least  one  that  is  supposed  to  be 
so,  as  it  has  never  been  decomposed.  It  is  always  found  united 
with  the  negative  electricity.  It  will  be  one  of  the  first  of  the 
elementary  bodies  whose  properties  I  shall  explain  to  you,  and, 
as  you  will  soon  perceive,  it  is  one  of  the  most  important  in 
nature  ;  but  it  would  be  irrelevant  to  enter  upon  this  subject  at 
present.  We  must  now  confine  our  attention  to  the  enumera- 
tion and  classification  of  the  simple  bodies  in  general.  They 
may 'be  arranged  as  follows  : 

CLASS  I. 

Comprehending  the  imponderable  agents,  viz. 

HEAT    OR    CALORIC, 

LIGHT, 

ELECTRICITY. 

*  No  actual  discovery  makes  this  probable.     It  is  supposing  that  alt 
Ihe  gases,  as  oxygen,  hydrogen,  <kc.  as  well  as  phosphorus,   sulphur, 
and  carbon  and  several  other  substances   are  in  part  composed  of  a 
metal,  and  yet  not  one  among  this  number  are  known  to  have  metallic 
bases.     C. 

*  Three  of  the  alkalies  only  are  known  to  have  metallic  base?,    € 


OP  CHEMISTRY, 

CLASS  II. 


Comprehending  agents  capable  of  uniting  with  inflammable, 
bodies,  and  in  most  instances  of  effecting  their  combustion* 


OXYGEN, 
CHLORINE, 

IODINE.* 


CLASS  III. 

Comprehending  bodies  capable  of  uniting  with  oxygen,  and 
forming  witli  it  various  compounds.  This  class  may  be  di- 
vided as  follows  : 

DIVISION    I. 

water. 

DIVISION    2. 

Bodies  forming  acids. 
NITROGEN,  .  .  .  forming  nitric  acid. 
SULPHUR,     .  .  .  forming"  sulphuric  acid. 
PHOSPHORUS,  .  .  forming  phosphoric  acid. 
CARBON,    ....  forming  carbonic  acid. 
BORACIUM,    .  .  .  forming  boracic  acid. 
FLUORiuivi,    . ..  .  forming  fluoric  acid. 
MURIATIUM,    .  .  forming  muriatic  acid^ 

DIVISION  3. 

Metalic  bodies  forming  alkalies. 
POTASSIUM,  .  .  .  forming  potash. 

SODIUM, forming  soda. 

AMMONIUM,   .  .  .  forming  ammonia- 
LITHIUM,    ....  forming  lithina.t 

DIVISION  4. 

Metallic  bodies  forming  earths. 
CALCIUM,  or  metal  forming  lime. 
MAGNIUM,    ....  forming  magnesia, 
»  BARIUM, forming  barytes. 

*  A  majority  of  the  most  learned  Chemists,  it  is  believed,  have 
Joubted  whether  Chlorine  and  Iodine  were  supporters  of  combustion, 
any  farther  than  they  contain  oxygen.  C« 

t  This  fourth  alkali  was  discovered  by  Mr,  Arfimdflon,  a  Swedish 
Chemist,  so  recently  as  the  year  1818* 


8  GENERAL    PRINCIPLES 

STRONTIUM,    .  .  .  forming  strontites 
SILICIUM,    ....  forming  silex. 
ALUMIUN,    ....  forming  aluinine, 
YTTRIUM,    ....  forming  yttria. 
GLUCIUM,    ....  forming  glucina. 
ZIRCONIUM,    .  .  .  forming  zirconia.* 

DIVISION  5. 

Metals,  either  naturally  metallic,  or  yielding  their  oxygen  to 
carbon  or  to  heat  alone. 

Subdivision  1. 

Malleable  metals. 

GOLD,  COPPER, 

PLATINA,  IRON, 

PALLADIUM,  LEAD, 

SILVER,f  NICKEL, 

MERCURY,!):  ZINC, 

TIN.  CADMIUM.^ 

Subdiv.  2. 
Brittle  metals. 

ARSENIC,  ANTIMONY, 

BISMUTH,    '  MANGANESE, 

TELLURIUM,  URANIUM, 

COBALT,  COLUMBIUM  Or  TAN- 
TUNGSTEN,  TALIUM, 

MOLYBDENUM,  IRIDIUM, 

TITANIUM,  OSMIUM, 

CHROME,  RHODIUM, 
CERIUN.JI 

*  Of  all  these  earths,  three  or  four  only  have  as  yet  been  distinctly 
decomposed. 

t  These  first  four  metals  have  commonly  been  distinguished  by  the 
appellation  of  perfect  or  noble  metals,  on  account  of  their  possessing  the 
characteristic  properties  of  ductility,  malleability,  inalterability,  and 
great  specific  gravity,  in  an  eminent  degree. 

^  Mercury,  in  its  liquid  state,  cannot,  of  course,  be  called  a  mallea- 
ble metal.  But  when  frozen,  it  possesses  a  considerable  degree  of  mal- 
leability. 

$  \  metal  resembling  tin;  which  was  discovered  in  1817,  in  an  ore 
of  zinc,  by  Mr.  Mromeyer. 

j|  These  last  four  or  five  metallic  bodies  are  placed  under  this  class 
for  the  sake  of  arrangement,  though" some  of  their  properties  have  not 
yet  fully  investigated. 


5F    CHEMISTRY. 

Caroline.  Oh,  what  a  formidable  list !  you  will  have  much 
to  do  to  explain  it,  Mrs.  B. ;  for  1  assure  you  it  is  perfectly  un- 
intelligible to  me,  and  I  think  rather  perplexes  than  assists  me. 

Mrs.  B.  Uo  not  let  that  alarm  you,  my  dear ;  I  hope  that 
hereafter  this  classification  will  appear  quite  clear,  and,  so  far 
from  perplexing  you,  will  assist  you  in  arranging  your  ideas, 
It  would  be  in  vain  to  attempt  forming  a  division  that  would 
appear  perfectly  clear  to  a  beginner  ;  for  you  may  easily  con- 
ceive that  a  chemical  division  being  necessarily  founded  on 
properties  with  which  you  are  almost  wholly  unacquainted,  it 
is  imposssible  that  you  should  at  once  be  able  to  understand  its 
meaning  or  appreciate  its  utility. 

But,  before  we  proceed  further,  it  will  be  necessary  to  give 
you  some  idea  of  chemical  attraction,  a  power  on  which  the 
whole  science  depends. 

Chemical  Attraction,  or  the  Attraction  of  Composition,  con- 
sists in  the  peculiar  tendency  which  bodies  of  a  different  nature 
have  to  unite  with  each  other.  It  is  by  this  force  that  all  the 
compositions,  and  decompositions,  are  effected. 

Emily.  What  is  the  difference  between  chemical  attraction, 
and  the  attraction  of  cohesion,  or  of  aggregation,  which  you  of- 
ten mentioned  to  us,  in  former  conversations  ? 

Mrs.  B.  The  attraction  of  cohesion  exists  only  between  par- 
ticles of  the  same  nature,  whether  simple  or  compound  ;  thus  it 
unites  the  particles  of  a  piece  of  metal  which  is  a  simple  sub- 
stance, and  likewise  the  particles  of  a  loaf  of  bread  which  is  a 
compound.  The  attraction  of  composition,  on  the  contrary  ? 
unites  and  maintains,  in  a  state  of  combination,  particles  of  a 
dissimilar  nature;  it  is  this  power  that  forms  each  of  the  com- 
pound particles  of  which  bread  consists  ;  and  it  is  by  the  attrac- 
tion of  cohesion  that  all  these  particles  are  connected  into  a 
single  mass. 

Emily.  The  attraction  of  cohesion,  then,  is  th^  power  which 
unites  the  integrant  particles  of  a  body  :  the  attraction  of  com- 
position that  which  combines  the  constituent  particles.  Is  it 
not  so  ? 

Mrs.  B.  Precisely  :  and  observe  that  the  attraction  of  cohe- 
sion unites  particles  of  a  similar  nature,  without  changing  their 
original  properties  ;  the  result  of  such  an  union,  therefore,  is  a 
body  of  the  same  kind  as  the  particles  of  which  it  is  formed ; 
whilst  the  attraction  of  composition,  by  combining  particles  of 
a  dissimilar  nature,  produces  compound  bodies,  quite  different 
from  any  of  their  constituents.  If  for  instance,  I  pour  on  the 
piece  of  copper,  contained  in  this  </Iass,  some  of  this  liquid 
(which  is  called  nitric  acid,)  for  which  it  has  a  strong  attrac- 


10  GENERAL  PRINCIPLES 

tion,  every  particle  of  the  copper  will  combine  with  a  particle 
of  acid,  and  together  they  will  form  a  new  body,  totally  differ- 
ent from  either  the  copper  or  the  acid. 

Do  you  observe  the  internal  commotion  that  already  begins 
to  take  place  ?  It  is  produced  by  ihe  combination  of  these  two 
substances,*  and  yet  the  acid  has  in  this  case  to  overcome  not 
only  the  resistance  which  the  strong  cohesion  of  the  particles  of 
copper  opposes  to  their  combination  with  it,  but  also  to  over- 
come the  weight  of  the  copper,  which  makes  it  sink  to  the  bot- 
tom of  the  glass,  and  prevents  the  acid  from  having  such  fr-ee 
access  to  it  as  it  would  if  the  metal  were  suspended  in  the  li- 
quid. 

Emily.  The  acid  seems,  however,  to  overcome  both  these 
obstacles  without  difficulty,  and  appears  to  be  very  rapidly  dis- 
solving the  copper. 

Mrs.  B.  By  this  means  it  reduces  the  copper  into  more  mi- 
nute parts  than  could  possibly  be  done  by  any  mechanical  pow- 
er. But  as  the  acid  can  act  only  on  the  surface  of  the  metal,  it 
will  be  some  time  before  the  union  of  these  two  bodies  will  be 
completed. 

You  may,  however,  already  see  how  totally  different  this 
compound  is  from  either  of  its  ingredients.  It  is  neither  colour- 
less, like  the  acid,  nor  hard,  heavy,  and  yellow  like  the  copper. 
If  you  tasted  it,  you  would  no  longer  perceive  the  sourness  of 
the  acid.  It  has  at  present  the  appearance  of  a  blue  liquid  ; 
but  when  the  union  is  completed,  and  the  water  with  which  the 
arid  is  diluted  is  evaporated,  the  compound  will  assume  the  form 
of  regular  crystals  of  a  fine  blue  colour,  and  perfectly  transpar- 
ent.! Of  these  I  can  show  you  a  specimen,  as  I  have  prepar- 
ed some  for  that  purpose. 

Caroline.  How  beautiful  they  are,  in  colour,  form,  and  trans- 
parency ! 

Emily.  Nothing  can  be  more  striking  than  this  example  of 
chemical  attraction. 

Mrs.  B.  The  term  attraction  has  been  lately  introduced  into 
chemistry  as  a  substitute  for  the  word  aflmity,to  which  some 

*  This  hardly  explains  the  process.  A  part  of  the  oxygen  of  the  ni- 
tric acid  unites  with  the  copper  ;  and  in  consequence  of  this  loss  of  ox- 
ysren,  the  nitric  acid  is  converted  into  nitrous  gas.  It  is  the  escape  of 
this  gas  through  the  water  as  it  is  formed  that  occasions  the  commo- 
tion. C. 

t  These  crystals  are  more  easily  obtained  from  a  mixture  of  sulphu- 
ric with  a  little  nitric  arid 4 

t  '•  h  -se  crystals  are  su.'phate  of  copper,  or  what  is  commonly  knowr 
nnder  the  name  of  blue  vitriol.  C, 


OP  CHEMISTRY.  1 

chemists  have  objected,  because  it  originated  in  the  vague  notion 
that  chemical  combinations  depended  upon  a  certain  resem- 
blance, or  relationship,  between  particles  that  are  disposed  to 
unite  5  and  this  idea  is  not  only  imperfect,  but  erroneous,  as  it 
is  generally  particles  of  the  most  dissimilar  nature,  that  have 
the  greatest  tendency  to  combine. 

Caroline.  Besides,  there  seems  to  be  no  advantage  in  using 
a  variety  of  terms  to  express. the  same  meaning;  on  the  con- 
trary it  creates  confusion;  and  as  we  are  well  acquainted  with 
the  term  Attraction  in  natural  philosophy,  we  had  better  adopt 
it  in  chemistry  likewise. 

Mrs.  B.  If  you  have  a  clear  idea  of  the  meaning,  I  shall 
leave  you  at  liberty  to  express  it  in  the  terms  you  prefer.  For 
myself,  I  confess  that  i  think  the  word  Attraction  best  suited 
to  the  general  law  that  unites  the  integrant  particles  of  bodies  ; 
and  Affinity  better  adapted  to  that  which  combines  the  constit- 
uent particles,  as  it  may  convey  an  idea  of  the  preference  which 
some  bodies  have  for  others,  which  the  term  attraction  of  com- 
position does  not  so  well  express. 

Emily.  So  I  think  ;  for  though  that  preference  may  not  re- 
sult from  any  relationship,  or  similitude,  between  the  particles 
(as  you  say  was  once  supposed,)  yet,  as  it  really  exists,  it  ought 
to  be  expressed. 

Mrs.  B.  Well,  let  it  be  agreed  that  you  may  use  the  terms 
affinity,  chemical  attraction,  and  attraction  of  composition^ 
indifferently,  provided  you  recollect  that  they  have  all  the  same 
meaning. 

Emily.  I  do  not  conceive  how  bodies  can  be  decomposed  by 
chemical  attraction.  That  this  power  should  be  the  means  of 
composing  them,  is  very  obvious ;  but  that  it  should,  at  the  same 
time,  produce  exactly  the  contrary  effect,  appears  to  me  very 
singular. 

Mrs.  B.  To  decompose  a  body  is,  you  know,  to  separate 
its  constituent  parts,  which,  as  we  have  just  observed,  cannot 
be  done  by  mechanical  means. 

Emily.  No :  because  mechanical  means  separate  only  the 
integrant  particles  ;  they  act  merely  against  the  attraction  of  co- 
hesion, and  only  divide  a  compound  into  smaller  parts. 

Mrs.  B.  The  decomposition  of  a  body  is  performed  by 
chemical  powers.  If  you  present  to  a  body  composed  of  two 
principles,  a  third,  which  has  a  greater  affinity  for  one  of 
them  than  the  two  first  have  for  each  other,  it  will  be  decompo- 
sed, that  is,  its  two  principles  will  be  separated  by  means  of 
the  third  body.  Let  us  call  two  ingredients,  of  which  the  body 
is  composed,  A  and  B.  If  we  present  to  it  another  ingredient 


12  GENERAL    PRINCIPLED 

C,  which  has  a  greater  affinity  for  B  than  that  which  unites  A 
and  B,  it  necessarily  follows  that  B  will  quit  A  to  combine  with 
C.  The  new  ingredient,  therefore,  has  effected  a  decomposition 
of  the  original  body  A  B ;  A  has  been  left  alone,  and  a  new 
compound,  B  C,  has  been  formed. 

Emily.  We  might,  I  think,  use  the  comparison  of  two 
friends,  who  were  very  happy  in  each  other's  society,  till  a 
third  disunited  them  by  the  preference  which  one  of  them  gave 
to  the  new-comer. 

Mrs.  B.  Very  well.  I  shall  now  show  you  how  this  takes 
place  in  chemistry. 

Let  us  suppose  that  we  wish  to  decompose  the  compound  we 
have  just  formed  by  the  combination  of  the  two  ingredients, 
copper  and  nitric  acid  ;  we  may  do  this  by  presenting  to  it  a 
piece  of  iron,  for  which  the  acid  has  a  stronger  attraction  than 
for  copper:  the  acid  will,  consequently  quit  the  copper  to  com- 
bine with  the  iron,  and  the  copper  will  be  what  the  chemists  call 
precipitated,  that  is  to  say,  it  will  be  thrown  down  in  its  sepa- 
rate state,  and  re-appear  in  its  simple  form. 

In  order  to  produce  this  effect,  I  shall  dip  the  blade  of  this 
knife  into  the  fluid,  and,  when  I  take  it  out,  you  will  observe, 
that,  instead  of  being  wetted  with  a  bluish  liquid,  like  that  con- 
tained in  the  glass,  it  will  be  covered  with  a  thin  coat  of  cop- 
per. 

Caroline.  So  it  is  really  !  but  then  is  it  not  the  copper,  in- 
stead of  the  acid,  that  has  combined  with  the  iron  blade  ? 

Mrs.  J3.  No ;  you  are  deceived  by  appearances :  it  is  the 
acid  which  combines  with  the  iron,  and,  in  so  doing,  deposits  or 
precipitates  the  copper  on  the  surface  of  the  blade. 

Emily.  But,  cannot  three  or  more  substances  combine  to- 
gether, without  any  of  them  being  precipitated  ? 

Mrs.  B.  That  is  sometimes  the  case  ;  but,  in  general,  the 
stronger  affinity  destroys  the  weaker  ;  and  it  seldom  happens 
that  the  attraction  of  several  substances  for  each  other  is  so 
equally  balanced  as  to  produce  such  complicated  compounds.* 

Caroline.  But,  pray,  Mrs.  B.,  what  is  the  cause  of  the  chem- 
ical attraction  of  bodies  for  each  other  ?  It  appears  to  me  more 
extraordinary  or  unnatural,  if  I  may  use  the  expression,  than 
the  attraction  of  cohesion,  which  unites  particles  of  a  similar 
nature. 

Mrs.  B.  Chemical  attraction  may,  like  that  0f  cohesion  or 

*  Such  compounds  are  quite  numerous.  They  are  called  triple  salt?. 
Alum  is  one.  It  is  composed  of  Alumine,  potash,  and  sulphuric  acid. 
Tartar  Emetic  is  another.  It  is  composed  of  tartaric  acid,  potash  and 
antimony.  C. 


OF  CHEMISTRY. 

gravitation,  be  one  of  the  powers  inherent  in  matter,  which,  in 
our  present  state  of  knowledge,  admits  of  no  other  satisfactory 
explanation  than  an  immediate  reference  to  a  divine  cause. 
Sir  H.  Davy,  however,  whose  important  discoveries  have  open- 
ed such  improved  views  in  chemistry,  has  suggested  an  hypo- 
thesis which  may  throw  great  light  upon  that  science.  He  sup- 
poses that  there  are  two  kinds  of  electricity,  with  one  or  other 
of  which  all  bodies  are  united.  These  we  distinguish  by  the 
names  of  positive  and  negative  electricity  ;  those  bodies  are 
disposed  to  combine,  which  possess  opposite  electricities,  as 
they  are  brought  together  by  the  attraction  which  these  electri- 
cities have  for  each  other.  But,  whether  this  hypothesis  be 
altogether  founded  on  truth  or  not,  it  is  impossible  to  question 
the  great  influence  of  electricity  in  chemical  combinations. 

Emily.  So,  that  we  must  suppose  that  the  two  electricities 
always  attract  each  other,  and  thus  compel  the  bodies  in  which 
they  exist  to  combine  ?* 

Caroline.  And  may  not  this  be  also  the  cause  of  the  attrac- 
tion of  cohesion  ? 

Mrs.  B.  No,  for  in  particles  of  the  same  nature  the  same 
electricities  must  prevail,  and  it  is  only  the  different  or  opposite 
electric  fluids  that  attract  each  other. 

Caroline.  These  electricities  seem  to  me  to  be  a  kind  of 
chemical  spirit,  which  animates  the  particles  of  bodies,  and 
draws  them  together. 

Emily.  If  it  is  known,  then,  with  which  of  the  electricities 
bodies  are  united,  it  can  be  inferred  which  will,  and  which  will 
not,  combine  together  ? 

Mrs.  B.  Certainly. — I  should  not  omit  to  mention,  that  some 
doubts  have  been  entertained,  whether  electricity  be  really  a 
material  agent,  or  whether  it  might  not  be  a  power  inherent  in 
bodies,  similar  to,  or  perhaps  identical  with,  attraction, 

*  There  seems  to  be  an  objection  to  this  theory  as  explained  here. 
When  two  bodies,  one  in  the  positive,  the  other  in  the ^egative state  of 
electricity  are  presented  to  each  other,  a  mutual  attraction  takes 
pla.ce,  until  they  touch,  or  come  within  the  striking  distance,  so 
that  the  electric  fluid  can  pass  from  the  positive  to  the  negative  body. 
When  this  is  effected,  they  are  said  to  be  in  a  state  of  equilibrium,  or 
in  the  same  state  of  electricity,  and  consequently  neither  attract  nor 
repel  each  other.  If  therefore,  chemical  attraction  depends  on  the 
different  electrical  states  of  the  particles,  w.e  are  still  at  a  loss  how  t» 
account  for  their  adhesion  even  after  they  are  united.  The  celebrated 
Kepler  accounted  for  the  affinity  of  particles  by  supposing  each  to  have 
its  likings  audits  antipathies,  and  the  power  of  choosing  accordingly. 
This  theory  only  wants  our  belief  to  make  it  satisfactory.  C, 

3 


*•*  L10HT. 

Emily.  But  what  then  would  be  the  electric  spark  which  is 
visible,  and,  must  therefore  be  really  material  ? 

Mrs.  B.  What  we  call  the  electric  spark,  may,  Sir  H.  Davy 
says,  be  merely  the  heat  and  light,  or  fire  produced  by  the 
chemical  combinations  with  which  these  phenomena  are  always 
connected.  We  will  not,  however,  enter  more  fully  on  this 
important  subject  at  present,  but  reserve  the  principal  facts 
which  relate  to  it  to  a  future  conversation. 

Before  we  part,  however,  I  must  recommend  you  to  fix  in 
your  memory  the  names  of  the  simple  bodies  against  our  next 
interview. 


CONVERSATION  II. 

ON  LIGHT  AND  HEAT,  OR  CALORIC. 

Caroline.  WE  have  learned  by  heart  the  names  of  all  the 
simple  bodies  which  you  have  enumerated,  and  we  are  now 
ready  to  enter  on  the  examination  of  each  of  them  successively, 
You  will  begin,  I  suppose,  with  LIGHT  ? 

Mrs.  B.  Respecting  the  nature  of  light  we  have  little  more 
than  conjectures.  It  is  considered  by  most  philosophers  as  a 
real  substance  immediately  emanating  from  the  sun,  and  from 
all  luminous  bodies,  from  which  it  is  projected  in  right  lines 
with  prodigious  velocity.  Light,  however,  being  imponderable, 
it  cannot  be  confined  and  examined  by  itself;  and  therefore  it 
is  to  the  effects  it  produces  on  other  bodies,  rather  than  to  its 
immediate  nature,  that  we  must  direct  our  attention. 

The  connection  between  light  and  heat  is  very  obvious  j 
indeed,  it  is  such,  that  it  is  extremely  difficult  to  examine  the 
one  independently  of  the  other. 

Emily.  But,  is  it  possible  to  separate  light  from  heat ;  I 
thought  they  were  only  different  degrees  of  the  same  thing,  fire  ? 

Mrs,  B.  I  told  you  that  fire  was  not  now  considered  as  a  sim- 
ple element.  Whether  light  and  heat  be  altogether  different  a- 
gents,  or  not,  I  cannot  pretend  to  decide ;  but,  in  many  cases,  light 
may  be  separated  from  heat.  The  first  discovery  of  this  was 
made  by  a  celebrated  Swedish  chemist,  Scheele.  Another  very 
striking  illustration  of  the  separation  of  heat  and  light  was 
Jong  after  pointed  out  by  Dr.  Herschell.  This  philosopher 
discovered  that  these  two  agents  were  emitted  in  the  rays  of  the 
£u.n3  and  that  heat  was  less  refrangible  than  light ;  for,  in  sep?.~ 


LIGHT.  id- 

rating  the  different  coloured  rays  ofjpight  by  a  prism  (as  we  did 
some  time  ago,)  he  found  that  the  greatest  heat  was  beyond  the 
spectrum,  at  a  little  distance  from  the  red  rays,  which,  you  may 
recollect  are  the  least  refrangible. 

Emily.  I  should  like  to  try  that   experiment. 

Mrs.  B.  It  is  by  no  means  an  easy  one :  the  heat  of  a  ray  of 
light,  refracted  by  a  prism,  is  so  small,  that  it  requires  a  very 
delicate  thermometer  to  distinguish  the  difference  of  the  degree 
of  heat  within  and  without  the  spectrum.  For  in  this  experi- 
ment the  heat  is  not  totally  separated  from  the  light,  each  col- 
oured ray  retaining  a  certain  portion  of  it,  though  the  greatest 
part  is  not  sufficiently  refracted  to  fall  within  the  spectrum.; 

Emily.  I  suppose,  then,  that  those  coloured  rays  which  are 
the  least  refrangible,  retain  the  greatest  quantity  of  heat  f 

Mrs.  B.  They  do  so. 

Emily.  Though  I  no  longer  doubt  that  light  and  heat  can 
be  separated,  Dr.  Herschell  s  experiment  does  not  appear -to 
me  to  afford  sufficient  proof  that  they  are  essentially  different ; 
for  light,  which  you  call  a  simple  body,  may  likewise  be  divi- 
ded into  the  various  coloured  rays. 

Mrs.  B.  No  doubt  there  must  be  some  difference  in  the  va- 
rious coloured  rays.  Even  their  chemical  powers  are  different. 
The  blue  rays,  for  instance,  have  the  greatest  effect  in  sepa-v 
jatin£  oxygen  from  bodies,  as  v/as  found  by  Scheele  ;  and  there 
exist  also,  as  Dr.  Wollaston  has  shown,  rays  more  refrangible 
than  the  blue,  which  produce  the  same  chemical  effect,  and, 
what  is  very  remarkable,  are  invisible.* 

Emily.  Do  you  think  it  possible  that  heat  may  be  merely  a 
modification  of  light  ? 

Mrs.  B.  That  is^a  supposition  which,  in  the  present  state  of 
natural  philosophy,  can  neither  be  positively  affirmed  nor  de- 
nied. Let  us,  therefore,  instead  of  discussing  theoretical 
points,  be  contented  with  examining  what  is  known  respecting 
the  chemical  effects  of  light. 

Light  is  capable  of  entering  into  a  kind  of  transitory  union 
with  certain  substances,  and  this  is  what  has  been  called  phos- 
phorescence. Bodies  that  are  possessed  of  this  property,  after 
being  exposed  to  the  sun's  rays,  appear  luminous  in  the  dark. 
The  shells  of  fish,  the  bones  of  land  animals,  marble,  limestone, 

*  The  violet  rays  have  the  power  of  imparting  the  magnetic  virtue 
to  steel.  The  process  consists  in  intercepting  all  the  rays  except  this, 
and  of  throwing  this,  being  first  collected  into  a  focus  by  a  lens,  on 
the  middle  of  a  needle,  and  tarrying  it  towards  the  extremity.  This 
is  to  be  done  many  times,  and  always  towards  the  same  extremity. 
After  a  while  the  needle  acquires  polarity.  C» 


1O  LIGHT. 

and  a  variety  of  combinations  of  earths,  are  more  or  kss  pow* 
er fully  phosphorescent. 

Caroline.  I  remember  being  much  surprised  last  summer 
with  the  phosphorescent  appearance  of  some  pieces  of  rotten 
wood,  which  had  just  been  dug  out  of  the  ground ;  trwy  shone 
so  bright  that  I  at  first  supposed  them  to  be  glow-worms. 

Emily.  And  is  not  the  light  of  a  glow-worm  of  a  phospho- 
rescent nature  ? 

Mrs.  B.  It  is  a  very  remarkable  instance  of  phosphorescence 
in  living  animals ;  this  property,  however,  is  not  exclusively 
possessed  by  the  glow-worm.  The  insect  called  the  lanthorn- 
fly,  which  is  peculiar  to  warm  climates,  emits  light  as  it  flies, 
producing  in  the  dark  a  remarkably  sparkling  appearance. 
But  it  is  more  common  to  see  animal  matter  in  a  dead  state  pos- 
sessed of  a  phosphorescent  quality ;  sea-fish  is  often  eminently 
so.* 

Emily.  I  have  heard  that  the  sea  has  sometimes  had  the  ap- 
pearance of  being  illuminated,  and  that  the  light  is  supposed  t» 
proceed  from  the  spawn  of  fishes  floating  on  its  surface. 

Mrs.  B.  This  light  is  probably  owing  to  that  or  some  other 
animal  matter.  Sea  water  has  been  observed  to  become  lumi- 
nous from  the  substance  of  a  fresh  herring  having  been  immers- 
ed in  it;  and  certain  insects,  of  the  Medusa  kind,  are  known  to 


produce  aimnw. '          •      ' 

But  the  strongest  phosphorescence  is  produced  by  cnemicai 
compositions  prepared  for  the  purpose,  the  most  common  of 
which  consists  of  oyster-shells  and  sulphur,  and  is  known  by 
the  name  of  Canton ?s  Phosphorus.! 

Emily.  I  am  rather  surprised,  Mrs.  B.,  that  you  should  have 
said  so  much  of  the  light  emitted  by  phosphorescent  bodies 
without  taking  any  notice  of  that  which  is  produced  by  burn- 
ing bodies. 

Mrs.  B.  The  light  emitted  by  the  latter  is  so  intimately  con- 
nected with  the  chemical  history  of  combustion,  that  I  must  de- 
fer all  explanation  of  it  till  we  come  to  the  examination  of  that 
process,  which  is  one  of  the  most  interesting  in  chemical  scr- 
ence. 

*  The  phosphorescence  of  dead  animals  is  owing  to  the  escape  of 
phosphorus  in  the  form  of  phosphoretted  hydrogen.  This  is  set  free 
from  its  combination  with  the  substance  of  the  animal  by  the  putre- 
factive fermentation  C. 

t  To  prepare  this,  mix  3  parts  of  oyster  shells  calcined  for  an  hour 
and  pulverized  with  1  part  of  sulphur.  This  is  to  be  rammed  into  a 
crucible,  which  is  to  be  kept  at  a  red  heat  for  one  hour.  On  exposing 
•ome  of  this  to  the  sun's  rays,  it  absorbs  light,  and  will  shine  in  the 
dark*  This  shows  that  light  can  be  separated  Jrorn  heat.  C. 


FREE  CALORIC.  If 

Light  is  an  agent  capable  of  producing  various  chemical 
changes.  It  is  essential  to  the  welfare  both  of  the  animal  and 
vegetable  kingdoms ;  for  men  and  plants  grow  pale  and  sickly 
if  deprived  of  its  salutary  influence.  It  is  likewise  remarkable 
for  its  property  of  destroying  colour,  which  renders  it  of  great 
consequence  in  the  process  of  bleaching. 

Emily.  Is  it  not  singular  that  light,  which  in  studying  optics 
we  were  taught  to  consider  as  the  source  and  origin  of  colours^ 
should  have  also  the  power  of  destroying  them  ? 

Caroline.  It  is  a  fact,  however,  that  we  every  day  experi- 
ence; you  know  how  it  fades  the  colours  of  linens  and  silks. 

Emily.  Certainly.  And  I  recollect  that  endive  is  made  to 
grow  white  instead  of  green,  by  being  covered  up  so  as  to  ex- 
clude the  light.  But  by  what  means  does  light  produce  these 
effects  ? 

Mrs.  B.  This  I  cannot  attempt  to  explain  to  you  until  you 
liave  obtained  a  further  knowledge  of  chemistry.  As  the  chem- 
ical properties  of  light  can  be  accounted  for  only  in  their  refer- 
ence to  compound  bodies,  it  would  be  useless  to  detain  you  any 
longer  on  this  subject ;  we  may  therefore  pass  on  to  the  exami- 
nation of  heat,  or  caloric,  with  which  we  are  somewhat  better 
acquainted. 

HEAT  and  LIGHT  may  be  always  distinguished  by  the  differ- 
ent sensations  they  produce.  Light  affects  the  sense  of  sight ; 
Caloric  that  of  feeling;  the  one  produces  Vision,  the  other  the 
sensation  of  Heat. 

Caloric  is  found  to  exist  in  a  variety  of  forms  or  modifica- 
tions, and  I  think  it  will  be  best  to  consider  it  under  the  two  fol- 
lowing heads,  viz. 

1.  FREE    OR    RADIANT    CALORIC. 

2.  COMBINED    CALORIC. 

The  first,  FREE  or  RADIANT  CALORIC,  is  also  called  HEAT 
OF  TEMPERATURE;  it  comprehends  all  heat  which  is  percepti- 
ble to  the  senses,  and  affects  the  thermometer. 

Emily.  You  mean  such  as  the  heat  of  the  sun,  of  fire,  of 
candles,  of  stoves;  in  short,  of  every  thing  that  burns? 

Mrs.  tt.  And  likewise  of  things  that  do  not  burn,  as,  for  in- 
stance, the  warmth  of  the  body ;  in  a  word,  all  heat  that  is 
sensible,  whatever  may  be  its  degree,  or  the  source  from  which 
it  is  derived. 

Caroline.  What  then  are  the  other  modifications  of  caloric  r 
It  must  be  a  strange  kind  of  heat  that  cannot  be  perceived  bv 
®ur  senses. 

3* 


18  FREE    CALORIC 

Mrs.  B.  None  of  the  modifications  of  caloric  should  pro  p - 
erly  be  called  heat ;  for  heat,  strictly  speaking,  is  the  sensati  on 
produced  by  caloric,  on  animated  bodies  ;  this  word,  therefore, 
in  the  accurate  language  of  science,  should  be  confined  to  ex- 
press the  sensation.  But  custom  has  adapted  it  likewise,  to  in- 
animate matter,  and  we  say  the  heat  of  an  oven,  the  heat  of 
the  sun,  without  any  reference  to  the  sensation  which  they  are 
capable  of  exciting. 

It  was  in  order  to  avoid  the  confusion,  which  arose  from  thus 
confounding  the  cause  and  effect,  that  modern  chemists  adopted 
the  new  word  caloric,  to  denote  the  principle  which  produces 
heat;  yet  they  do  not  always,  in  compliance  with  their  own 
language,  limit  the  word  heat  to  the  expression  of  the  sensa- 
tion, since  they  still  frequently  employ  it  in  reference  to  the  oth- 
er modifications  of  caloric  which  are  quite  independent  of  sen- 
sation. * 

Caroline.  But  you  have  not  yet  explained  to  us  what  these 
other  modifications  of  caloric  are. 

Mrs.  B.  Because  you  are  not  acquainted  with  the  properties 
«f  free  caloric,  and  you  know  that  we  have  agreed  to  proceed 
with  regularity. 

One  of  the  most  remarkable  properties  of  free  caloric  is  its 
power  of  dilating  bodies.  This  fluid  is  so  extremely  subtle, 
that  it  enters  and  pervades  all  bodies  whatever,  forces  itself  be- 
tween their  particles,  and  not  only  separates  them,  but  fre- 
quently drives  them  asunder  to  a  considerable  distance  from 
each  other.  It  is  thus  that  caloric  dilates  or  expands  a  body  so 
as  to  make  it  occupy  a  greater  space  than  it  did  before. 

Emily.  The  effect  it  has  on  bodies,  therefore,  is  directly 
contrary  to  that  of  the  attraction  of  cohesion  ;  the  one  draws 
the  particles  together,  the  other  drives  them  asunder. 

Mrs.  B.  Precisely.  There  is  a  continual  struggle  between 
the  attraction  of  aggregation,  and  the  expansive  power  of  calo- 
ric ;  and  from  the  action  of  these  two  opposite  forces,  result  all 
the  various  forms  of  matter,  or  degrees  of  consistence,  from  the 
solid  to  the  liquid  and  aeriform  state.  And  accordingly  we  find 
that  most  bodies  are  capable  of  passing  from  one  of  these  forms 
to  the  other,  merely  in  consequence  of  their  receiving  different 
quantities  of  caloric. 

*  If  I  touch  a  body  at  a  higher  temperature  than  my  hand.  I  imme- 
diately receive  a  quantity  of  caloric  from  it,  and  at  the  same  instant 
feel  'h-  sensation  called  heat.  The  caloric  then  is  the  cause  of  this 
teasation,  and  heat  the  effect  of  caloric  passing  into  my  hand.  C, 


FREE   CALORIC.  19 

Caroline.  That  is  very  curious ;  but  I  think  I  understand 
the  reason  of  it.  If  a  great  quantity  of  caloric  is  added  to  a 
solid  body,  it  introduces  itself  between  the  particles  in  such  a 
manner  as  to  overcome,  in  a  considerable  degree,  the  attraction 
of  cohesion ;  and  the  body,  from  a  solid,  is  then  converted  into 
a  fluid. 

Mrs.  B.  This  is  the  case  whenever  a  body  is  fused  or  melted  ; 
but  if  you  add  caloric  to  a  liquid,  can  you  tell  me  what  is  the 
consequence  ? 

Caroline.  The  caloric  forces  itself  in  greater  abundance  be- 
tween the  particles  of  the  fluid,  and  drives  them  to  such  a  dis- 
tance from  each  other,  that  their  attraction  of  aggregation  is 
wholly  destroyed  :  the  liquid  is  then  transformed  into  vapour. 
Mrs.  B.  Very  well ;  and  this  is  precisely  the  case  with 
boiling  water,  when  it  is  converted  into  steam  or  vapour,  and 
with  all  bodies  that  assume  an  aeriform  state. 

Emily.  1  do  not  well  understand  the  word  aeriform  ? 
Mrs.  B.  Any  elastic  fluid  whatever ;  whether  it  be  merely 
vapour  or  permanent  air,  is  galled  aeriform. 

But  each  of  these  various  Sates,  solid,  liquid,  and  aeriform, 
admit  of  many  different  degrees  of  density,  or  consistence,  still 
arising  (chiefly  at  least)  from  the  different  quantises  of  caloric 
the  bodies  contain.  Solids  are  of  various  degrees  of  density, 
from  that  of  gold,  to  that  of  a  thin  jelly.  Liquids,  from 
the  consistence  of  melted  glue,  or  melted  metals,  to  that  of 
ether,  which  is  the  lightest  of  all  liquids.  The  different  elas- 
tic fluids  (with  which  you  are  not  yet  acquainted)  are  sus- 
ceptible of  no  less  variety  in  their  degrees  of  density. 

Emily.  But  does  not  every  individual  body  also  admit  of 
different  degress  of  consistence,  without  changing  its  state  ? 

Mrs.  B.  Undoubtedly;  and  this  I  can  immediately  show 
you  by  a  very  simple  experiment.  This  piece  of  iron  now  ex- 
actly fits  the  frame,  or  ring,  made  to  receive  it  5  but  if  heated 
red  hot,  it  will  no  longer  do  so,  for  its  dimensions  will  be  so 
much  increased  by  the  caloric  that  has  penetrated  into  it,  that 
it  will  be  much  too  large  for  the  fra  -e. 

The  iron  is  now  red  hot ;  by  applying  it  to  the  frame,  we 
shall  see  how  much  it  is  dilated. 

Emily.  Considerably  so  indeed  !  I  knew  that  heat  had  this 
effect  on  bodies,  but  I  did  not  imagine  that  it  could  be  made 
so  conspicuous. 

Mrs.  B.  By  means  of  this  instrument  (called  a  Pyrometer) 
we  may  estimate,  in  the  most  exact  manner,  the  various  dilata- 
tions of  any  solid  body  by  heat.  The  body  we  are  now  going 
to  submit  to  trial  is  this  small  iron  bar ;  I  fix  it  to  this  appara- 


20  FREE    CALORIC, 

tus,  (PLATE  I.  Fig.  1.)  and  then  heat  it  by  lighting  the  three 
lamps  beneath  it :  when  the  bar  expands,  it  increases  in  length 
as  well  as  thickness ;  and,  as  one  end  communicates  with  this 
wheel- work ,  whilst  the  other  end  is  fixed  and  immoveable,  no 
sooner  does  it  begin  to  dilate  than  it  presses  against  the  wheel- 
work,  and  sets  in  motion  the  index,  which  points  out  the  de- 
grees of  dilatation  on  the  dial- plate. 

Emily.  This  is,  indeed,  a  very  curious  instrument ;  but  I  do 
not  understand  the  use  of  the  wheels :  would  it  not  be  more 
simple,  and  answer  the  purpose  equally  well,  if  the  bar  in  dila* 
ting,  pressed  against  the  index,  and  put  it  in  motion  without  the 
intervention  of  the  wheels  ? 

Mrs.  B.  The  use  of  the  wheels  is  merely  to  multiply  the  mo- 
tion, and  therefore  render  the  effect  of  the  caloric  more  obvious ; 
for  if  the  index  moved  no  more  than  the  bar  increased  in  length, 
its  motion  would  scaicely  be  perceptible;  but  by  means  of  the 
wheels  it  moves  in  a  much  greater  proportion,  which  therefore 
renders  the  variations  far  more  conspicuous. 

By  submitting  different  bodies  to,  the  test  of  the  pyrometer,  it 
is  found  that  they  are  far  from  dffating  in  the  same  proportion. 
Different  metals  expand  in  different  degrees,  and  other  kinds  of 
solid  bodies  ^arf  still  more  in  this  respect.  But  this  different 
susceptibility  of  dilation  is  still  more  remarkable  in  fluids  than 
in  solid  bodies,  as  I  shall  show  you.  I  have  here  two  glass 
tubes,  terminated  at  one  end  by  large  bulbs.  We  shall  fill  the 
bulbs,  the  one  with  spirit  of  wine,  the  other  with  water.  I 
have  coloured  both  liquids,  in  order  that  the  effect  may  be  more 
conspicuous.  The  spirit  of  wine,  you  see,  dilates  by  the 
warmth  of  my  hand  as  I  hold  the  bulb.* 

Emily.  It  certainly  does,  for  I  see  it  is  rising  into  the  tube. 
But  water,  it  seems,  is  not  so  easily  affected  by  heat ;  for  scarce- 
ly any  change  is  produced  on  it  by  the  warmth  of  the  hand. 

Mrs.  b.  True  ;  we  shall  now  plunge  the  bulbs  into  hot  water, 
(PLATE  I.  Fig.  2.)  and  you  will  see  both  liquids  rise  in  the 
tubes  ;  but  the  spirit  of  wine  will  ascend  highest. 

Caroline.  How  rapidly  it  expands  !  Now  it  has  nearly  reach- 
ed the  top  of  the  tube,  though  the  water  has  hardly  begun  to 
rise. 

Emily.  The  water  now  begins  to  dilate.  Are  not  these  glass 
tubes,  with  liquids  rising  within  them,  very  like  thermometers  ? 

*  In  the  absence  of  glass  tubes  terminated  by  bulbs,  procure  a  pair 
of  tin  cannisters,  3  inches  high  and  2  wide,  soldered  up  all  round.  la 
the  middle  of  the  top  of  each,  have  inserted  a  circular  tin  spout,  and  in- 
fo these  cement  glass  tubes  about  J2  inches  high.  These  will  answer 
every  purpose,  C. 


FREE    CALORIC.  21 

Mrs.  B.  A  thermometer  is  constructed  exactly  on  the  same 
principle,  and  these  tubes  require  only  a  scale  to  answer  the 
purpose  of  thermometers  :  but  they  would  be  rather  awkward 
in  their  dimensions.  The*  tubes  and  bulbs  of  thermometers, 
though  of  various  sizes,  are  in  general  much  smaller  than  these  ; 
the  tube  too  is  hermetically*  closed,  and  the  air  excluded  from 
it.  The  fluid  most  generally  used  in  thermometers  is  mercury, 
commonly  called  quicksilver,  the  dilatations  and  contractions  of 
which  correspond  more  exactly  to  the  additions,  and  subtrac- 
tions, of  caloric,  than  those  of  any  other  fluid. 

Caroline.  Yet  I  have  often  seen  coloured  spirit  of  wine  used 
in  thermometers. 

Mrs.  B.  The  expansions  and  contractions  of  that  liquid  are 
not  quite  so  uniform  as  those  of  mercury  ;  but  in  cases  in  which 
it  is  not  requisite  to  ascertain  the  temperature  with  great  pre- 
cision, spirit  of  wine  will  answer  the  purpose  equally  well,  and 
indeed  in  some  respects  better,  as  the  expansion  of  the  latter  is 
greater,  and  therefore  more  conspicuous.  This  fluid  is  used 
likewise  in  situations  and  experiments  in  which  mercury  would 
be  frozen ;  for  mercury  becomes  a  solid  body,  like  a  piece  of 
lead  or  any  other  metal,  at  a  certain  degree  of  cold  ;  but  no 
degree  of  cold  has  ever  been  known  to  freeze  spirit  of  wine.t 

A  thermometer,  therefore,  consists  of  a  tube  with  a  bulb, 
such  as  you  see  here,  containing  a  fluid  whose  degrees  of  dila- 

•  *r\  which  the 
canon  anu  cumittcuon  are  ^indicated  by  a  Scale  v~ 

tube  is  fixed.  The  degree  which  indicates  the  boiling  point, 
simply  means  that,  when  the  fluid  is  sufficiently  dilated  to  rise 
to  this  point,  the  heat  is  such  that  water  exposed  to  the  same 
temperature  will  boil.  When,  on  the  other  hand,  the  fluid  is 
so  much  condensed  as  to  sink  to  the  freezing  point,  we  know 
that  water  will  freeze  at  that  temperature.  The  extreme  points 
of  the  scales  are  not  the  same  in  all  thermometers,  nor  are  the 
degrees  always  divided  in  the  same  manner.  In  different 
countries  philosophers  have  chosen  to  adopt  different  scales 
and  divisions.  The  two  thermometers  most  used  are  those  of 
Fahrenheit,  and  of  Reaumur  ;  the  first  is  generally  preferred 
by  the  English,  the  latter  by  the  French. 

Emily.  The  variety  of  scale  must  be  very  inconvenient,  and 

* 

*  The  tube  is  closed  by  holding  the  end  over  a  spirit  lamp  until  the 
glass  is  melted.  This  wora  is  derived  from  Hermes,  the  Greek  name 
forAiertury.  He  is  said  to  have  been  the  mventer  of  chemistry ; 
hence  this  is  sometimes  called  the  Hermetic  art,  and  hermetically, 'or 
chemically  closed,  is  closed  by  heat  or  melting.  C. 

t  Spiiit  of  wine  is  stated  to  have  been  frozen  in  England  by  some 
process  which  the  author  has  preferred  to  keep  secret.  C. 


tfKEE    CALORIC. 

1  should  think  liable  to  occasion  confusion,  when  French  and 
English  experiments  are  compared. 

Mrs.  B.  The  inconvenience  is  but  very  trifling,  because  the 
different  gradations  of  the  scales  do  not  affect  the  principle  up- 
on which  thermometers  are  constructed.  When  we  know,  for 
instance,  that  Fahrenheit's  scale  is  divided  into  212  degrees, 
in  which  32U  corresponds  with  the  freezing  point,  and  212° 
with  the  point  of  boiling  water;  and  that  Reaumur's  is  divided 
only  into  80  degrees,  in  which  0°  denotes  the  freezing  point, 
and  80°  that  of  boiling  water,  it  is  easy  to  compare  the  two 
scales  together,  and  reduce  the  one  into  the  other.  But,  for 
greater  convenience,  thermometers  are  sometimes  constructed 
with  both  these  scales,  one  on  either  side  of  the  tube  ;  so  that 
the  correspondence  of  the  different  degrees  of  the  two  scales  is 
thus  instantly  seen..  Here  is  one  of  these  scales,  (PLATE  II. 
Fig.  l.)  by  which  you  can  at  once  perceive  that  each  degree  of 
Reaumur's  corresponds  to  2  1-4  of  Fahrenheit's  division.  But 
I  believe  the  French  have,  of  late,  given  the  preference  to  what 
they  call  the  centigrade  scale,  in  which  the  space  between  the 
freezing  and  the  boiling  point  is  divided  into  100  degrees. 

Caroline.  That  seems  to  me  the  most  reasonable  division, 
and  I  cannot  guess  why  the  freezing  point  is  called  32°,  or 
what  advantage  is  derived  from  it. 

Mrs.  B.  There  really  is  no  advantage  in  it  5  anditQiigina- 
ted  in  «  mistaken  opinion  of  the  instrument-maker,  Fahrenheit, 
who  first  constructed  these  thermometers.  He  mixed  snow  and 
salt  together,  and  produced  by  that  means  a  degree  of  cold 
which  he  concluded  was  the  greatest  possible,  and  therefore 
made  his  scale  begin  from  that  point.  Between  that  and  boil- 
ing water  he  made  212  degrees,  and  the  freezing  point  was 
found  to  be  at  32o. 

Emily.  Are  spirit  of  wine,  and  mercury,  the  only  liquids 
used  in  the  construction  of  thermometers  ? 

Mrs.  B.  I  believe  they  are  the  only  liquids  now  in  use,  though 
some  others,  such  as  linseed  oil,  would  make  tolerable  thermom- 
eters: but  for  experiments  in  which  a  very  quick  and  delicate 
test  of  the  changes  of  temperature  is  required,  air  is  !he  fluid 
sometimes  employed.  The  bulb  of  air  thermometers  is  filled 
with  common  air  only,  and  its  expansion  and  contraction  are* 
indicated  by  a  small  drop  of  any  coloured  liquor,  which  is  sus- 
pended within  the  tube,  and  moves  up  and  down,  according  as 
the  air  within  the  bulb  and  tube  expands  or  contracts.  But  in 
general,  air  thermometers,  however  sensible  to  changes  of  tem- 
perature, are  by  no  means  accurate  in  their  indications. 

I  can,  however,  show  you  an  air  thermometer  of  a  very  pe- 


PLATE  //. 


TIIKRAtOMEJ'KR . 


TREE    CALORIC. 

ouliar  construction,  which  is  remarkably  well  adapted  for  some 
chemical  experiments,  as  it  is  equally  delicate  and  accurate  in 
its  indications.  * 

Caroline.  It  looks  like  a  double  thermometer  reversed,  the 
tube  being  bent,  and  having  a  large  bulb  at  each  of  its  extremi- 
ties. (PLATE  11.  Fig.  2.) 

Emily.  Why  do  you  call  it  an  air  thermometer ;  the  tube 
contains  a  coloured  liquid  ? 

Mrs.  b*  But  observe  that  the  bulbs  are  filled  with  air,  the  li- 
quid being  confined  to  a  portion  of  the  tube,  and  answering  on- 
ly the  purpose  of  showing,  by  its  motion  in  the  tube,  the  com- 
parative dilatation  or  contraction  of  the  air  within  the  bulbs? 
which  afford  an  indication  of  their  relative  temperature.  Thus 
if  you  heat  the  bulb  A,  by  the  warmth  of  your  hand,  the  fluid 
will  rise  towards  the  bulb  B,  and  the  contrary  will  happen  if 
you  reverse  the  experiment. 

But  if,  on  the  contrary,  both  tubes  are  of  the  same  tempera- 
ture, as  is  the  case  now,  the  coloured  liquid,  suffering  an  equal 
pressure  on  each  side,  no  change  of  level  takes  place. 

Caroline.  This  instrument  appears,  indeed,  uncommonly 
delicate.  The  fluid  is  set  in  motion  by  the  mere  approach  of 
my  hand. 

Mrs.  B.  You  must  observe,  however,  that  this  thermometer 
cannot  indicate  the  temperature  of  any  particular  body,  or  of 
the  medium  in  which  it  is  immersed  ;  it  serves  only  to  point 
out  the  difference  of  temperature  between  the  two  bulbs,  when 
placed  under  different  circumstances.  For  this  reason  it  has 
been  called  differential  thermometer.  You  will  see  hereafter 
to  what  particular  purposes  this  instrument  applies. 

Emily.  But  do  common  thermometers  .indicate  the  exact 
quantity  of  caloric  contained  either  in  the  atmosphere,  or  in  any 
body  with  which  they  are  in  contact  ?t 

*  Students  in  chemistry  may  amuse  themselves  with  air  thermome- 
ters of  their  own  construction.  Procure  a  flat  vial,  or  inkstand  with 
a  wide  inouth;  also  a  broken  thermometer  tube,  the  bulb  being  entire. 
Fit  a  cork  air  tight  to  the  vial,  and  pierce  it  in  the  middle  with  a  hot 
iron  to  admit  the  tube  Fill  the  vial  about  hair'  full  of  some  coloured 
liquid.  Warm  the  bulb  of  the  tube  by  holding  it  in  the  hand,  and  in 
this  state  introduce  the  small  end  through  the  cork  nearly  to  the  bot- 
tom of  the  vial.  The  hand  being  removed  f-om  the  bulb,  the  fluid 
will  rise  in  the  tube.  The  fluid  will  afterwards  rise  or  fall  as  heat  is 
applied  to  the  vial  or  bulb.  C. 

t  The  thermometer  indicates  the  exact  quantity  of  free  caloric  pres- 
ent at  the  time  and  place  of  the  experiment.  Thus  if  a  certain  quantity 
of  heat  is  required  to  raise  the  mercury  £0°,  double  this  quantity  will 
raise  it  to  40°.  AH  bodies  contain  a  quantity  of  heat  not  appreciable 


24  .  FREE    CALORIC. 

Mrs.  B.  No  :  first,  because  there  are  other  modifications  ol 
caloric  which  do  not  affect  the  thermometer ;  and,  secondly, 
because  the  temperature  of  a  body,  as  indicated  by  the  ther- 
mometer, is  only  relative.  When,  for  instance,  the  thermome- 
ter remains  stationary  at  the  freezing  point,  we  know  that  the 
atmosphere  (or  medium  in  which  it  is  placed,  whatever  it  may 
be)  is  as  cold  as  freezing  water  ;  and  when  it  stands  at  the  boil- 
ing point,  we  know  that  this  medium  is  as  hot  as  boiling  water ; 
but  we  do  not  know  the  positive  quantity  of  heat  contained  either 
in  freezing  or  boiling  water,  any  more  than  we  know  the  real  ex- 
tremes of  heat  and  cold ;  and  consequently  we  cannot  deter- 
mine that  of  the  body  in  which  the  thermometer  is  placed. 
Caroline.  I  do  not  quite  understand  this  explanation. 
Mrs.  /»'.  Let  us  compare  a  thermometer  to  a  well,  in  which 
the  water  rises  to  different  heights,  according  as  it  is  more  or 
less  supplied  by  the  spring  which  feeds  it ;  if  the  depth  of  the 
well  is  unfathomable,  it  must  be  impossible  to  know  the  abso- 
lute quantity  of  water  it  contains  ;  yet  we  can  with  the  greatest 
accuracy  measure  the  number  of  feet  the  water  has  risen  or 
fallen  in  the  well  at  any  time,  and  consequently  know  the  pre- 
cise quantiiy  of  its  increase  or  diminution,  without  having  the 
least  knowledge  of  the  whole  quantity  of  water  it  contains.* 

Caroline.  Now  I  comprehend  it  very  well ;  nothing  appears 
to  me  to  explain  a  thing  so  clearly  as  a  comparison. 

Emily.  But  will  thermometers  bear  any  degree  of  heat  ? 
Mrs.  B.  No ;  for  if  the  temperature  were  much  above  the 
highest  degree  marked  on  the  scale  of  the  thermometer,  the 
mercury  would  burst  the  tube  in  an  attempt  to  ascend.  And  at 
any  rate,  no  thermometer  can  be  applied  to  temperatures  high- 
er than  the  boiling  point  of  the  liquid  used  in  its  construction, 
for  the  steam,  on  the  liquid  beginning  to  boil,  would  burst  the 
tube.  In  furnaces,  or  whenever  any  very  high  temperature  is 
to  be  measured,  a  pyrometer,  invented  by  Wedgwood,  is  used 
for  that  purpose.  It  is  made  of  a  certain  composition  of  baked 

by  the  thermometer,  or  sensible  to  the  touch.  This  is  called  Jixed  or 
latem  heat.  This  can  sometimes  be  set  fiee,  as  when  we  hammer  a 
piece  of  cold  iron  it  becomes  hot.  Thus  the  latent  caloric  is  squeezed 
out  of  the  iron  by  the  contraction  of  its  pores  under  the  hammer,  and  it 
then  becomes/ree  caloric.  C. 

*  This  passage  may  be  expounded  as  follows.  The  unfathomable 
depth  of  the  well  signifies  the  absolute  quantity  of  caloric,  and  which 
the  thermometer  does  not  measure  ;  because  all  bodies  however  cold, 
still  contain  caloric.  Thus  mercur3r  freezes  at  40°  below  zero,  but 
Still  contains  caloric,  and  so  on.  The  rising  and  falling  of  the  water 
signifies  the  greater  or  less  quantity  of  free  caloric  as  indicated  by  the 
thermometer.  C. 


FREE    CALORIC.  25 

clay,  which  has  the  peculiar  property  of  contracting  by  heat,  so 
that  the  degree  of  .contraction  of  this  substance  indicates  the 
temperature  to  which  it  has  been  exposed. 

Emily.  But  is  it  possible  for  a  body  to  contract  by  heat  t  I 
thought  that  heat  dilated  all  bodies  whatever. 

Mrs.  B.  This  is  not  an  exception  to  the  rule.  You  must  re- 
collect that  the  bulk  of  the  clay  is  not  compared,  whilst  hot, 
with  that  which  it  has  when  cold  5  but  it  is  from  the  change 
which  the  clay  has  undergone  by  having  been  heated  that  the 
indications  of  this  instrument  are  derived.  This  change  con* 
sists  in  a  beginning  fusion  which  tends  to  unite  the  particles 
of  clay  more  closely.,  thus  rendering  it  less  pervious  or  spon- 
gy-* " 

Clay  is  to  be  considered  as  a  spongy  body,  abounding  in  in- 
terstices or  pores,  from  its  having  contained  water  when  soft. 
These  interstices  are  by  heat  lessened,  and  would  by  extreme 
heat  be  entirely  obliterated. 

Caroline.  And  how  do  you  ascertain  the  degrees  of  contrac- 
tion of  Wedgwood's  pyrometer  ? 

Mrs.  B.  The  dimensions  of  the  piece  of  clay  are  measured  by 
a  scale  graduated  on  the  side  of  a  tapered  groove,  formed  in  a 
brass  ruler  5  the  more  the  clay  is  contracted  by  the  heat,  the 
further  it  will  descend  into  the  narrow  part  of  the  tube. 

Before  we  quit  the  subject  of  expansion,  I  must  observe  to 
you  that,  as  liquids  expand  more  readily  than  solids,  so  elastic 
fluids,  whether  air  or  vapour,  are  the  most  expansible  of  all  bod- 
ies. 

It  may  appear  extraordinary  that  all  elastic  fluids  whatever, 
undergo  the  same  degree  of  expansion  from  equal  augmenta- 
tions of  temperature. 

Emily.  I  suppose,  then,  that  all  elastic  fluids  are  of  the  same 
density  ? 

Mrs.  B.  Very  far  from  it ;  they  vary  in  density,  more  thaw 
either  liquids  or  solids.  The  uniformity  of  their  expansibility, 
which  at  first  may  appear  singular,  is,  however,  readily  accoun- 
ted for.  For  if  the  different  susceptibilities  of  expansion  of 
bodies  arise  from  their  various  degrees  of  attraction  of  cohe- 
sion, no  such  difference  can  be  expected  in  elastic  fluids,  since 
in  these  the  attraction  of  cohesion  does  not  exist,  their  particles 
being  on  the  contrary  possessed  of  an  elastic  or  repulsive  pow-r 

*  According  to  the  calculation's  of  Saussure,  the  temperature  necessa- 
ry to  melt  this  clay  is  1575°  Wedgwood,  which  is  a  degree  of  heat 
greatly  beyond  our  common  furnaces.  It  is  therefore  most  probable 
that  the  clay  contracts  at  lower  temperatures  by  the  los?  of  mois- 
ture, C. 

4 


-6  FREE    CALO&IC. 

er ;  they  will  therefore  all  be  equally  expanded  by  equal  de- 
grees of  caloric. 

Emily.  True ;  as  there  is  no  power  opposed  to  the  expan- 
sive force  of  caloric  in  elastic  bodies,  its  effect  must  be  the  same 
in  all  of  them. 

Mrs.  B.  Let  us  now  proceed  to  examine  the  other  properties 
of  free  caloric. 

Free  caloric  always  tends  to  diffuse  itself  equally,  that  is  to 
say,  when  two  bodies  are  of  different  temperatures,  the  warm- 
er gradually  parts  with  its  heat  to  the  colder,  till  they  are7  both 
brought  to  the  same  temperature.  Thus,  when  a  thermometer 
is  applied  to  a  hot  body,  it  receives  caloric ;  when  to  a  cold  one, 
it  communicates  part  of  its  own  caloric,  and  this  communica- 
tion continues  until  the  thermometer  and  the  body  arrive  at  the 
same  temperature. 

Emily.  Cold,  then,  is  nothing  but  a  negative  quality,  simply 
implying  the  absence  of  heat. 

Mrs.  B.  Not  the  total  absence,  but  a  diminution  of  heat  ; 
for  we  know  of  no  body  in  which  some  caloric  may  not  be  dis- 
covered. 

Caroline.  But  when  I  lay  my  hand  on  this  marble  table,  I 
feel  it  positively  cold,  and  cannot  conceive  that  there  is  any 
caloric  in  it. 

Mrs.  B.  The  cold  you  experience  consists  in  the  loss  of  calo- 
ric that  your  hand  sustains  in  an  attempt  to  bring  its  tempera- 
ture to  an  equilibrium  with  the  marble.  If  you  lay  a  piece  of 
ice  upon  it,  you  will  find  that  the  contrary  effect  will  take 
place  ;  the  ice  will  be  melted  by  the  heat  it  abstracts  from  the 
marble. 

Caroline.  Is  it  not  in  this  case  the  air  of  the  room,  which 
being  warmer  than  the  marble,  melts  the  ice  ? 

Mrs.  B.  The  air  certainly  acts  on  the  surface  which  is  ex- 
posed to  it,  but  the  table  melts  that  part  with  which  it  is  in 
contact. 

Caroline.  But  why  does  caloric  tend  to  an  equilibrium  ?  It 
cannot  be  on  the  same  principle  as  other  fluids,  since  it  has  no 
weight  ? 

Mrs.  B.  Very  true,  Caroline,  that  is  an  excellent  objection. 
You  might  also,  with  some  propriety,  object  to  the  term  equi- 
librium being  applied  to  a  body  that  is  without  weight ;  but  I 
know  of  no  expression  that  would  explain  my  meaning  so  well. 
You  must  consider  it,  however,  in  a  figurative  rather  than  a 
Iheral  sense  :  its  strict  meaning  is  an  equal  diffusion.  We 
Cannot,  indeed,  well  say  by  what  power  it  diffuses  itself  equally, 
though  it  is  not  surprising  that  it  should  go  from  the  parts 


FREE    CALORIC.  27 

which  have  the  most  to  those  which  have  the  least.  This  sub- 
ect  is  best  explained  by  a  theory  suggested  by  Professor  Pre* 
vost  of  Geneva,  which  is  now,  I  believe,  generally  adopted. 

According  to  this  theory,  caloric  is  composed  of  particles 
perfectly  separate  from  each  other,  every  one  of  which  moves 
with  a  rapid  velocity  in  a  certain  direction.  These  directions 
vary  as  much  as  imagination  can  conceive,  the  result  of  which 
is,  that  there  are  rays  or  lines  of  these  particles  moving  with 
immense  velocity  in  every  possible  direction.  Caloric  is  thus 
universally  diffused,  so  that  when  any  portion  of  space  hap- 
pens to  be  in  the  neighbourhood  of  another,  which  contains 
more  caloric,  the  colder  portion  receives  a  quantity  of  calorific 
rays  from  the  latter,  sufficient  to  restore  an  equilibrium  of  tem- 
perature. This  radiation  does  not  only  take  place  in  free 
:>pace,  but  extends  also  to  bodies  of  every  kind.*  Thus  you 
may  suppose  all  bodies  whatever  constantly  radiating  caloric  : 
those  that  are  of  the  same  temperature  give  out  and  absorb 
equal  quantities,  so  that  no  variation  of  temperature  is  produced 
in  them  ;  but  when  one  body  contains  more  free  caloric  than 
another,  the  exchange  is  always  in  favour  of  the  colder  body, 
until  an  equilibrium  is  effected  5  this  you  found  to  be  the  case 
when  the  marble  table  cooled  your  hand,  and  again  when  it 
melted  the  ice. 

Caroline.  This  reciprocal  radiation  surprises  me  extremely  ; 
I  thought,  from  what  you  first  said,  that  the  hotter  bodies  alone 
emitted  rays  of  caloric  which  were  absorbed  by  the  colder  \ 
for  it  seems  unnatural  that  a  hot  body  should  receive  any  calor- 
ic from  a  cold  one,  even  though  it  should  return  a  greater  quan- 
tity. 

Mrs.  B.  It  may  at  first  appear  so,  but  it  is  no  more  extraor- 
dinary than  that  a  candle  should  send  forth  rays  of  light  to  the 
sun,  which,  you  know,  must  necessarily  happen. 

Caroline.  Well,  Mrs.  B — ,  Ibelieve'that  I  must  give  up  the 
point.  But  I  wish  I  could  see  these  rays' of  caloric;  I  should 
then  have  greater  faith  in  them. 

Mrs.  B.  Will  you  give  no  credit  to  any  sense  but  that  of 
sight  ?  You  may  feel  the  rays  of  caloric  which  you  receive 
from  any  body  of  a  temperature  higher  than  your  own  ;  the 
loss  of  the  caloric  you  part  with  in  return,  it  is  true,  is  not  per- 
ceptible ;  for  as  you  gain  more  than  you  lose,  instead  of  suffer- 
ing a  diminution,  you  are  really  making  an  acquisition  of  calo- 

*  This  is  true  when  applied  to  inanimate  matter.  But  if  a  live  ani- 
mal is  exposed  to  a  degree  of  heat  above  the  temperature  of  its  own. 
body,  it  has  the  power  of  resistance  ;  a<id  though  the  heat  he  100  de- 
grees above  that  of  the  animal,  it  scarcely  affects  its  temperature.  C. 


'28  FREE    CALOBltr. 

ric.  It  is,  therefore,  only  when  you  are  parting  with  it  to  « 
body  of  a  lower  temperature,  that  you  are  sensible  of  the  sen- 
sation of  cold,  because  you  then  sustain  an  absolute  loss  of  ca- 
loric. 

Emily.  And  in  this  case  we  cannot  be  sensible  of  the  small 
quantity  of  heat  we  receive  in  exchange  from  the  colder  body, 
because  it  serves  only  to  diminish  the  loss. 

Mrs.  B.  Very  well,  indeed,  Emily.  Professor  Picket,  oi 
Geneva,  has  made  some  very  interesting  experiments,  which 
prove  not  only  that  caloric  radiates  from  all  bodies  whatever, 
but  that  these  rays  may  be  reflected,  according  to  the  laws  of 
optics,  in  the  same  manner  as  light.  I  shall  repeat  these  ex- 
periments before  you,  having  procured  mirrors*  fit  for  the  pur- 
pose ;  and  it  will  afford  us  an  opportunity  of  using  the  differen- 
tial thermometer,  which  is  particularly  well  adapted  for  these 
experiments. — I  place  an  iron  bullet,  (PLATE  III.  Fig.  1.) 
about  two  inches  in  diameter,  and  heated  to  a  degree  not  suffi- 
cient to  render  it  luminous,  in  the  focus  of  this  large  metallic 
concave  mirror.  The  rays  of  heat  which  fall  on  this  mirror 
are  reflected,  agreeably  to  the  property  of  concave  mirrors,  in 
a  parallel  direction,  so  as  to  fall  on  a  similar  mirror,  which, 
you  see,  is  placed  opposite  to  the  first,  at  the  distance  of  about 
ten  feet;  thence  the  rays  converge  to  the  focus  of  the  second 
mirror,  in  which  I  place  one  of  the  bulbs  of  this  thermometer. 
Now,  observe  in  what  manner  it  is  affected  by  the  caloric  which 
is  reflected  on  it  from  the  heated  bullet. — The  air  is  dilated  in 
the  bulb  which  we  placed  in  the  focus  of  the  mirror,  and  the 
liquor  rises  considerably  in  the  opposite  leg. 

Emily.  But  would  not  the  same  effect  take  place,  if  the  rays 
of  caloric  from  the  heated  bullet  fell  directly  on  the  ther- 
mometer, without  the  assistance  of  the  mirrors  ? 

Mrs.  B.  The  effect  would  in  that  case  be  so  trifling,  at  the 
distance  at  which  the  bullet  and  the  thermometer  are  from  each 
uther,  that  it  would  be  almost  imperceptible.  The  mirrors, 
you  know,  greatly  increase  the  effect,  by  collecting  a  large 
quantity  of  rays  into  a  focus  ;  place  your  hand  in  the  focus  of 
the  mirror,  and  you  will  find  it  much  hotter  there  than  when 
you  remove  it  nearer  to  the  bullet. 

Emily.  That  is  very  true  ;  it  appears  extremely  singular   to 

*  Mirrors  made  of  common  tinned  iron  show  this  experiment  very 
well.  They  may  be  10  or  12  inches  in  diameter,  and  about  2  inches 
deep.  They  must  be  planished  with  a  hammer  having  a  convex  face, 
and  afterwards  polished  with  a  piece  of  buckskin,  and  a  little  whi- 
ting. C. 


(  01 

?M 


-< 


III 


lit 


^  i  * 
<-J^ 


S'AEE    CALORIC.  29 

feel  the  heat  diminish  in  approaching  the  body  from  which  it 
proceeds. 

Caroline.  And  the  mirror  which  produces  so  much  heat,  by 
converging  the  rays,  is  itself  quite  cold 

Mrs.  B.  The  same  number  of  rays  that  are  dispersed  over 
the  surface  of  the  mirror  are  collected  by  it  into  the  focus  j 
but  if  you  consider  how  large  a  surface  the  mirror  presents  to 
the  rays,  and,  consequently,  how  much  they  are  diffused  in 
comparison  to  what  they  are  at  the  focus,  which  is  little  more 
than  a  point,  I  think  you  can  no  longer  wonder  that  the  focus 
should  be  so  much  hotter  than  the  mirror. 

The  principal  use  of  the  mirror  in  this  experiment  is,  to 
prove  that  the  calorific  emanation  is  reflected  in  the  same  man- 
ner as  light. 

Caroline.  And  the  result,  T  think,  is  very  conclusive. 

Mrs.  tt.  The  experiment  may  be  repeated  with  a  wax  taper 
instead  of  the  bullet,  with  a  view  of  separating  the  light  from 
the  caloric.  For  this  purpose  a  transparent  plate  of  glass  must 
be  interposed  between  the  mirrors ;  for  light,  you  know,  passes 
with  great  facility  through  glass,  whilst  the  transmission  of  cal- 
oric is  almost  wholly  impeded  by  it.  We  shall  find,  however, 
in  this  experiment,  that  some  few  of  the  calorific  rays  pass 
through  the  glass  together  with  the  light,  as  the  thermometer 
rises  a  little  ;  but,  as  soon  as  the  glass  is  removed,  and  a  free 
passage  left  to  the  caloric,  it  will  rise  considerably  higher. 

Emily.  This  experiment,  as  well  as  that  of  Dr.  ilersdiell's, 
proves  that  light  and  heat  may  be  separated  ;  for  in  the  latter 
experiment  the  separation  was  not  perfect,  any  more  than  in 
that  of  Mr.  Pictet. 

Caroline.  I  should  like  to  repeat  this  experiment,  with  the 
difference  of  substituting  a  cold  body  instead  of  a  hot  one,  to 
see  whether  cold  would  not  be  reflected  as  well  as  heat. 

Mrs.  H.  That  experiment  wfcs  proposed  to  Mr.  Pictet  by  an 
incredulous  philosopher  like  yourself,  and  he  immediately  tried 
it  by  substituting  a  piece  of  ice  in  the  place  o>  th^  heated  bullet. 

Caroline.  Well,  Mrs.  B.,  and  what  was  the  result  ? 

Mrs.  B.  That  we  shall  see  ;  I  have  procured  some  ice  for 
the  purpose. 

Emily.  The  thermometer  falls  considerably  ! 

Caroline.  And  does  not  that  prove  that  cold  is  not  merely  a 
negative  quality,  implying  simply  an  inferior  degree  of  heat  ? 
The  cold  must  be  positive,  since  it  is  capable  of  reflection. 

Mrs.  w.  So  it  at  first  appeared  to  Vlr.  Pictet  ;  but  upon  a 
Httle  consideration  he  found  that  it  afforded  only  an  additional 

4* 


SO  PEEE    CALORIC* 

proof  of  the  reflection  of  heat :  this  I  shall  endeavour  to  explain 
to  you. 

According  to  Mr.  Prevost's  theory,  we  suppose  that  all  bo- 
dies whatever  radiate  caloric ;  the  thermometer  used  in  these 
experiments  therefore  emits  calorific  rays  in  the  same  manner  as 
any  other  substance.  When  its  temperature  is  in  equilibrium 
with  that  of  the  surrounding  bodies,  it  receives  as  much  caloric 
as  it  parts  with,  And  no  change  of  temperature  is  produced. 
But  when  we  introduce  a  body  of  a  lower  temperature,  such  as 
a  piece  of  ice,  which  parts  with  less  caloric  than  it  receives., 
the  consequence  is,  that  its  temperature  is  raised,  whilst  that  of 
the  surrounding  bodies  is  proportionally  lowered. 

Emily.  If,  for  instance,  I  was  to  bring  a  large  piece  of  ke 
into  this  room,  the  ice  would  in  time  be  melted,  by  absorbing 
caloric  from  the  general  radiation  which  is  going  on  throughout 
the  room  ;  and  as  it  would  contribute  very  little  caloric  in  re- 
turn for  what  is  absorbed,  the  room  would  necessarily  be  cool- 
ed by  it. 

Mrs.  B.  Just  so  ;  and  as  in  consequence  of  the  mirrors,  a 
inore  considerable  exchange  of  rays  takes  place  between  the 
ice  and  the  thermometer,  than  between  these  and  any  of  the 
surrounding  bodies,  the  temperature  of  the  thermometer  must 
be  more  lowered  than  that  of  any  other  adjacent  object. 

Caroline.  I  confess  I  do  not  perfectly  understand  your  ex- 
planation. 

Mrs.  B.  This  experiment  is  exactly  similar  to  that  made  with 
the  heated  bullet :  for,  if  we  consider  the  thermometer  as  the 
hot  body  (which  it  certainly  is  in  comparison  to  the  ice,)  you 
may  then  easily  understand  that  it  is  by  the  loss  of  the  calorific 
rays  which  the  thermometer  sends  to  the  ice,  and  not  by  any 
cold  rays  received  from  it,  that  the  fall  of  the  mercury  is  oc- 
casioned :  for  the  ice,  far  frorr  emitting  rays  of  cold,  sends 
forth  rays  of  caloric,  which  diminish  the  loss  sustained  by  the 
thermometer. 

Let  us  say,  for  instance,  that  the  radiation  of  the  thermome- 
ter towards  the  ice  is  equal  to  20,  and  that  of  the  ice  towards 
the  thermometer  to  10  :  the  exchange  in  favour  of  the  ice  is  as 
20  is  to  10,  or  the  thermometer  absolutely  loses  10,  whilst  the 
ice  gains  10. 

Caroline.  But  if  the  ice  actually  sends  rays  of  caloric  to  the 
thermometer,  must  not  the  latter  fall  still  lower  when  the  ice  is 
removed  ? 

Airs.  B.  No  ;  for  the  space  which  the  ice  occupied,  admits 
vays  from  all  the  surrounding  bodies  to  pass  through  it ;  and 
those  being  of  the  same  temperature  as  the  thermometer,  will 


FREE    CALORIC.  81 

not  affect  it,  because  as  much  heat  now  returns  to  the  thermom- 
eter as  radiates  from  it. 

Caroline.  I  must  confess  that  you  have  explained  this  in  so 
satisfactory  a  manner,  that  I  cannot  help  being  convinced  now 
that  cold  has  no  real  claim  to  the  rank  of  a  positive  being. 

Mrs.  B.  Before  I  conclude  the  subject  of  radiation  I  must 
observe  to  you,  that  different  bodies  (or  rather  surfaces)  possess 
the  power  of  radiating  caloric  in  very  different  degrees. 

Some  curious  experiments  have  been  made  by  Mr.  Leslie  on 
this  subject,  and  it  was  for  this  purpose  that  he  invented  the 
differential  thermometer;  with  its  assistance  he  ascertained  that 
black  surfaces  radiate  most,  glass  next,  and  polished  surfaces 
the  least  of  all. 

Emily.  Supposing  these  surfaces,  of  course,  to  be  all  of  the 
same  temperature. 

Undoubtedly.  I  will  now  show  you  the  very  simple  and 
ingenious  apparatus,  by  means  of  which  he  made  these  experi- 
ments. This  cubical  tin  vessel,  or  canister,  has  each  of  its 
sides  externally  covered  with  different  materials ;  the  one  is 
simply  blackened  ;  the  next  is  covered  with  white  paper ;  the 
third  with  a  pane  of  glass,  and  in  the  fourth  the  polished  tin 
surface  remains  uncovered.  We  shall  fill  this  vessel  with  hot 
water,  so  that  there  can  be  no  doubt  but  that  all  its  sides  will  be 
of  tiie  same  temperature.  Now  let  us  place  it  in  the  focus  of 
one  of  the  mirrors,  making  each  of  its  sides  front  it  in  succes- 
sion. We  shall  begin  with  the  black  surface.* 

Caroline.  It  makes  the  thermometer  which  is  in  the  focus  of 
the  other  mirror  rise  considerably — Let  us  turn  the  paper  sur- 
face towards  the  mirror.  The  thermometer  falls  a  little,  there- 
fore of  course  this  side  cannot  emit  or  radiate  so  much  caloric 
as  the  blackened  side. 

Emily.  This  is  very  surprising  ;  for  the  sides  are  exactly  of 
the  same  size,  and  must  be  of  the  same  temperature.  But  let 
us  try  the  glass  surface. 

Mrs.  B.  The  thermometer  continues  falling,  and  with  the 
plain  surface  it  falls  still  lower ;  these  two  surfaces  therefore 
radiate  less  and  less. 

Caroline.  I  think  I  have  found  out  the  reason  of  this. 

Mrs.  a.  I  should  be  very  happy  to  hear  it,  for  it  has  not  yet 
(to  my  knowledge)  been  accounted  for. 

*  The  radiating  power  of  different  surfaces  may  be  shown  thus.  Take 
a  common  half  pint  tin  cup,  scour  one  side  bright,  and  paint  or  smoke 
the  other  black.  Place  this  in  the  focus  of  the  mirror,  and  the  thermo- 
meter will  rise  or  fall  as  its  sides  are  changed.  U. 


FflEE    CALORIC. 

Caroline.  The  water  within  the  vessel  gradually  cools,  and 
the  thermometer  in  consequence  gradually  falls. 

Mrs.  B.  It  is  true  that  the  water  cools,  but  certainly  in  much 
less  proportion  than  the  thermometer  descends,  as  you  willper- 
eeive  if  you  now  change  the  tin  surface  for  the  black  one. 

Caroline.  I  was  mistaken  certainly,  for  the  thermometer  ri- 
ses again  now  that  the  black  surface  fronts  the  mirror. 

Mrs.  B.  And  yet  the  water  in  the  vessel  is  still  cooling, 
Caroline. 

Emily.  I  am  surprised  that  the  tin  surface  should  radiate  the 
least  caloric,  for  a  metallic  vessel  filled  with  hot  water,  a  silver 
tea-pot,  for  instance,  feels  much  hotter  to  the  hand  than  one  of 
black  earthenware. 

Mrs.  B.  That  is  owing  to  the  different  power  which  various 
bodies  possess  for  conducting'  caloiic,  a  property  which  we 
shall  presently  examine.  Thus,  although  a  metallic  vessel 
feels  warmer  to  the  hand,  a  vessel  of  this  kind  is  known  to 
preserve  the  heat  of  the  liquid  within,  better  than  one  of  any 
other  materials  ;  it  is  for  this  reason  that  silver  tea-pots  make 
better  tea  than  those  of  earthen  ware. 

Emily.  According  to  these  experiments,  light-coloured  dress- 
es, in  cold  weather,  should  keep  us  warmer  than  black  clothes, 
since  the  latter  radiate  so  much  more  than  the  former. 

Mrs.  B.  And  that  is  actually  the  case. 

Emily.  This  property,  of  different  surfaces  to  radiate  in  dif- 
ferent degrees,  appears  to  me  to  be  at  variance  with  the  equilib- 
rium of  caloric ;  since  it  would  imply  that  those  bodies  which 
radiate  most,  must  ultimately  become  coldest. 

Suppose  that  we  were  to  vary  this  experiment,  by  using  two 
metallic  vessels  full  of  boiling  water,  the  one  blackened,  the 
other  not ;  would  not  the  black  one  cool  the  first  ? 

Caroline.  True ;  but  when  they  were  both  brought  down  to 
the  temperature  of  the  room,  the  interchange  of  caloric  between 
the  canisters  and  the  other  bodies  of  the  room  being  then  equal, 
their  temperatures  would  remain  the  same. 

Emily.  I  do  not  see  why  that  should  be  the  case  ;  for  if  dif- 
ferent surfaces  of  the  same  temperature  radiate  in  different  de- 
grees when  heated,  why  should  they  not  continue  to  do  so  when 
cooled  down  to  the  temperature  of  the  room  ? 

Mrs.  B.  You  have  started  a  difficulty,  Emily,  which  cer- 
tainly requires  explanation.  It  is  found  by  experiment,  that 
the  power  of  absorption  corresponds  with  and  is  proportional 
to  that  of  radiation  ;  so  that  under  equal  temperatures,  bodies 
compensate  for  the  greater  loss  they  sustain  in  consequence  of 
their  greater  radiation  by  their  greater  absorption  ;  so  that  if 


KREE    CALORIG.  33 

you  were  to  make  your  experiment  in  an  atmosphere  heated 
like  the  canisters,  to  the  temperature  of  boiling  water,  though 
it  is  true  that  the  canisters  would  radiate  in  different  degrees,  no 
change  of  temperature  would  be  produced  in  them,  because 
they  would  each  absorb  caloric  in  proportion  to  their  respective 
radiation. 

Emily.  But  would  not  the  canisters  of  boiling  water  also  ab- 
sorb caloric  in  different  degrees  in  a  room  of  the  common  tem- 
perature ? 

Mrs.  B.  Undoubtedly  they  would.  But  the  various  bodies 
in  the  room  would  not,  at  a  lower  temperature,  (urnish  either 
of  the  canisters  with  a  sufficiency  of  caloric  to  compensate  for 
the  loss  they  undergo  ;  for,  suppose  the  black  canister  to  ab- 
sorb 400  rays  of  caloric,  whilst  the  metallic  one  absorbed  only 
200  5  yet  if  tine  former  radiate  800,  whilst  the  latter  radiates 
only  400,  the  black  canister  will  be  the  first  cooled  down  to  the 
temperature  of  the  room.  But  from  the  moment  the  equilibri- 
um of  temperature  has  taken  place,  the  black  canister,  both 
receiving  and  giving  out  400  rays,  and  the  metallic  one  200,  no 
change  of  temperature  will  take  place. 

Emily.  I  now  understand  it  extremely  well.  But  what  be- 
comes of  the  surplus  of  calorific  rays,  which  good  radiators 
emit  and  bad  radiators  refuse  to  receive  :  they  must  wander 
about  in  search  of  a  resting-place  ? 

Mrs.  B.  They  really  do  so  ;  for  they  are  rejected  and  sent 
back,  or,  in  other  words,  reflected  by  the  bodies  which  are 
bad  radiators  of  caloric  :  and  they  are  thus  transmitted  to  other 
bodies  which  happen  to  lie  in  their  way,  by  which  they  are  eith- 
er absorbed  or  again  reflected,  according  as  the  property  of  re- 
flection, or  that  of  absorption,  predominates  in  these  bodies. 

Caroline.  I  do  not  well  understand  the  difference  between 
yadiating  and  reflecting  caloric,  for  the  caloric  that  is  reflected 
from  a  body  proceeds  from  it  in  straight  lines,  and  may  surely 
be  said  to  radiate  from  it  ? 

Mrs.  B.  It  is  true  that  there  at  first  appears  to  be  a  great 
analogy  between  radiation  and  reflection,  as  they  equally  con- 
vey the  idea  of  the  transmission  of  caloric. 

But  if  you  consider  a  little,  you  will  perceive  that  when  a 
body  radiates  caloric,  the  heat  which  it  emits  not  only  pro- 
ceeds from,  but  has  its  origin  in  the  body  itself.  Whilst  when 
a  body  reflects  caloric,  it  parts  with  none  of  its  own  caloric, 
but  only  reflects  that  which  it  receives  from  other  bodies. 

Emily.  Of  this  difference  we  have  very  striking  examples 
before  us,  in  the  tin  vessel  of  water,  and  the  concave  mirrors  5 


34  FilEE    CALORIC. 

the  first  radiates  its  own  heat,  the  latter  reflect  the  heat  which 
they  receive  from  other  bodies. 

Caroline.  Now,  that  I  understand  the  difference,  it  no  longer 
surprises  me  that  bodies  which  radiate,  or  part  with  their  own 
caloric  freely,  should  not  have  the  power  of  transmitting  with 
equal  facility  that  which  they  receive  from  other  bodies. 

Emily.  Yet  no  body  can  be  said  to  possess  caloric  of  its 
own,  if  all  caloric  is  originally  derived  from  the  sun. 

Mrs.  B.  When  I  speak  of  a  body  radiating  its  own  caloric, 
I  mean  that  which  it  has  absorbed  and  incorporated  either  im- 
mediately from  the  sun's  rays,  or  through  the  medium  of  any 
other  substance. 

Caroline.  It  seems  natural  enough  that  the  power  of  absorp- 
tion should  be  in  opposition  to  that  of  reflection,  for  the  more 
caloric  a  body  receives,  the  less  it  will  reject. 

Emily.  And  equally  so  that  the  power  of  radiation  should 
correspond  with  that  of  absorption.  It  is,  in  fact,  cause  and 
effect  5  for  a  body  cannot  radiate  heat  without  having  previous- 
ly absorbed  it  5  just  as  a  spring  that  is  well  fed  flows  abun- 
dantly. 

Mrs.  B.  Fluids  are  in  general  very  bad  radiators  of  caloric  ; 
and  air  neither  radiates  nor  absorbs  caloric  in  any  sensible  de- 
cree 

!5     CC'  § 

We  have  not  yet  concluded  our  observations  on  free  caloric. 
But  I  shall  defer,  till  our  next  meeting,  what  I  have  further  to 
say  on  this  subject.  I  believe  it  will  afford  us  ample  conversa- 
tion for  another  interview. 


COiWERSATION  III. 

CONTINUATION  OF  THE  SUBJECT. 

Mm.  B.  IN  our  last  conversation,  we  began  to  examiin  the 
tendency  of  caloric  to  restore  an  equilibrium  of  temperature. 
Tnis  property  when  once  well  understood,  affords  the  explana- 
tion of  a  great  variety  of  facts  which  appeared  formerly  unac- 
countable. You  must  observe,  in  the  first  place,  that  the  ofli'd 
of  this  tendency  is  gradually  to  bring  all  bodies  that  are  in  con- 
tact to  the  same  temperature.  Thus  the  fire  which  burns  in 
the  grate,  communicates  its  heat  from  one  object  to  another, 
till  every  part  of  the  room  has  an  equal  proportion  of  it. 

Emily.  And  yet  this  book  is  not  so  cold  as  the  table  on 


FREE  CALORIC.  35 

which  it  lies,  though  both  are  at  an  equal  distance  from  the  fire, 
and  actually  in  contact  with  each  other,  so  that,  according  to 
your  theory,  they  should  be  exactly  df  the  same  temperature. 

'Caroline.  And  the  hearth,  which  is  much  nearer  the  fire 
than  the  carpet,  is  certainly  the  colder  of  the  two. 

Mrs.  B.  If  you  ascertain  the  temperature  of  these  several 
bodies  by  a  thermometer  (which  is  a  much  more  accurate  test 
than  your  feeling,)  you  will  find  that  it  is  exactly  the  same. 

Caroline.  But  if  they  are  of  the  same  temperature,  why 
should  the  one  feel  colder  than  the  other  ? 

Mr*.  B.  The  hearth  and  the  table  feel  colder  than  the  car- 
pet or  the  book,  because  the  latter  are  not  such  good  conductors 
of  heat  as  the  former.  Caloric  finds  a  more  easy  passage 
through  marble  and  wood,  than  through  leather  and  worsted  ; 
the  two  former  will  therefore  absorb  heat  more  rapidly  from 
your  hand,  and  consequently  give  it  a  stronger  sensation  of  cold 
than  the  two  latter,  although  they  are  all  of  them  really  of  the 
same  temperature. 

Caroline.  So,  then,  the  sensation  I  feel  on  touching  a  cold 
body,  is  in  proportion  to  the  rapidity  with  which  my  hand 
yields  its  heat  to  that  body  ? 

Mrs.  B.  Precisely  ;  and  if  you  lay  your  hand  successively 
on  every  object  in  the  room,  you. will  discover  which  are  good, 
and  which  are  bad  conductors  of  heat,  by  the  different  degrees 
of  cold  which  you  feel.  But  in  order  to  ascertain  this  point,  it 
is  necessary  that  the  several  substances  should  be  of  the  same 
temperature,  which  will  not  be  the  case  with  those  that  are 
very  near  the  fire,  or  those  that  are  exposed  to  a  current  of  cold 
air  from  a  window  or  door. 

Emily.  But  what  is  the  reason  that  some  bodies  are  better 
conductors  of  heat  than  others  ? 

]\Irs.  B.  This  is  a  point  not  well  ascertained.  It  has  been 
conjectured  that  a  certain  union  or  adherence  takes  place  be- 
tween the  caloric  and  the  particles  of  the  body  through  which  it 
passes.  If  this  adherence  be  strong*  the  body  detains  the  heat, 
and  parts  with  it  slowly  and  reluctantly ;  if  slight,  it  propa- 
gates it  freely  and  rapidly.  The  conducting  power  of  a  body 
is  therefore,  inversely,  as  its  tendency  to  unite  with  caloric. 

Emily.  That  is  to  say  that  the  best  conductors  are  those  that 
have  the  least  affinity  for  caloric. 

Mrs.  B.  Yes ;  but  the  term  affinity  is  objectionable  in  this 
case,  because,  as  that  word  is  used  to  express  a  chemical  at- 
traction (which  can  be  destroyed  only  by  decomposition,)  it 
cannot  be  applicable  to  the  slight  and  transient  union  that  takes 
place  between  free  caloric  and  the  bodies  through  which  it  pass- 


36  FREE  CALORIC 

es  ;  an  union  which  is  so  weak,  that  it  constantly  yields  to  tiit 
tendency  which  caloric  has  to  an  equilibrium.  Now  you 
clearly  understand,  that  the  passage  of  caloric,  through  bodies 
that  are  good  conductors,  is  much  more  rapid  than  through 
those  that  are  bad  conductors,  and  that  the  former  both  give 
and  receive  it  more  quickly,  and  therefore,  in  a  given  time, 
more  abundantly,  than  bad  conductors,  which  makes  them  feel 
cither  hotter  or  colder,  though  they  may  be,  in  fact,  both  of  the 
same  temperature. 

Caroline.  Yes,  I  understand  it  now  ;  the  table,  and  the  book 
lying  upon  it,  being  really  of  the  same  temperature,  would  each 
receive,  in  the  same  space  of  time,  the  same  quantity  of  heat 
from  my  hand,  were  their  conducting  powers  equal  ;  but  as  the 
table  is  the  best  conductor  of  the  two,  it  will  absorb  the  heat 
from  my  hand  more  rapidly,  and  consequently  produce  a 
stronger  sensation  of  cold  than  the  book. 

Mrs.  jB.  Very  well,  my  dear;  and  observe,  likewise,  that  if 
you  were  to  heat  the  table  and  the  book  an  equal  number  of 
degrees  above  the  temperature  of  your  body,  the  table,  which 
before  felt  the  colder,  would  now  feel  the  hotter  of  the  two  ; 
for,  as  in  the  first  case  it  took  the  heat  most  rapidly  from  your 
hand,  so  it  will  now  impart  heat  most  rapidly  to  it.  Thus  the 
marble  table,  which  seerns  to  us  colder  than  the  mahogany  one, 
will  prove  the  hotter  of  the  two  to  the  ice  ;  for,  if  it  takes  heat 
more  rapidly  from  our  hands,  which  are  warmer,  it  will  give 
out  heat  more  rapidly  to  the  ice,  which  is  colder.  Do  you  un- 
derstand the  reason  of  these  apparently  opposite  effects  ? 

Emily.  Perfectly.  A  body  which  is  a  good  conductor  of 
caloric,  affords  it  a  free  passage ;  so  that  it  penetrates  through 
that  body  more  rapidly  than  through  one  vyhich  is  a  bad  con- 
ductor ;  and  consequently,  if  it  is  colder  than  your  hand,  you 
lose  more  caloric,  and  if  it  is  hotter,  you  gain  more  than  with  a 
bad  conductor  of  the  same  temperature. 

Mrs.  ij.  But  you  must  observe  that  this  is  the  case  only  when 
the  conductors  are  either  hotter  or  colder  than  your  hand;  for, 
if  you  heat  different  conductors  to  the  temperature  of  your  bo- 
dy, they  will  all  feel  equally  warm,  since  the  exchange  of  cal- 
oric between  bodies  of  the  same  temperature  is  equal.  Now, 
can  you  tell  me  why  flannel  clothing,  which  is  a  very  bad  con- 
ductor of  heat,  prevents  our  feeling  cold  ? 

Caroline.  It  prevents  the  cold  from  penetrating 

Mrs.  B.  But  you  forget  that  cold  is  only  a  negative  quality. 

Caroline.  True  ;  it  only  prevents  the  heat  of  our  bodies  from 
escaping  so  rapidly  as  it  would  otherwise  do. 

.  B>  Now  you  have  explained  it  right ;  the  flannel  rather 


FREE    CALORIC,  37 

keeps  in  the  heat,  than  keeps  out  the  cold.  Were  the  atmos- 
phere of  a  higher  temperature  than  our  bodies,  it  would  be 
equally  efficacious  in  keeping  their  temperature  at  the  same 
degree,  as  it  would  prevent  the  free  access  of  the  external  heat, 
by  the  difficulty  with  which  it  conducts  it. 

Emily.  This?  I  think,  is  very  clear.  Heat,  whether  exter- 
nal or  internal,  cannot  easily  penetrate  flannel  ;  therefore  in 
cold  weather  it  keeps  us  warm,  and  if  the  weather  were  hotter 
than  our  bodies,  it  would  keep  us  cool. 

Mrs.  B.  The  most  dense  bodies  are,  generally  speaking,  the 
best  conductors  of  heat ;  probably  because  the  denser  the  body 
the  greater  are  the  number  of  points  or  particles  that  come  in 
contact  with  caloric.  At  the  common  temperature  of  the  at- 
mosphere, a  piece  of  metal  will  feel  much  colder  than  a  piece 
of  wood,  and  the  latter  than  a  piece  of  woollen  cloth ;  this 
again  will  feel  colder  than  flannel  ;  and  down,  which  is  one  of 
the  lightest,  is  at  the  same  time  one  of  the  warmest  bodies.* 

Caroline.  This  is,  I  suppose,  the  reason  that  the  plumage 
of  birds  preserve  them  so  effectually  from  the  influence  of  cold 
in  winter  ? 

Mrs.  B.  Yes ;  but  though  feathers  in  general  are  an  excellent 
preservative  against  cold,  down  is  a  kind  of  plumage  peculiar 
to  aquatic  birds,  and  covers  their  chest,  which  is  the  part  most 
exposed  to  the  water  ;  for  though  the  surface  of  the  water  is  not 
of  a  lower  temperature  than  the  atmosphere,  yet,  as  it  is  a  bet- 
ter conductor  of  heat,  it  feels  much  colder,  consequently  the 
chest  of  the  bird  requires  a  warmer  covering,  than  any  other 
part  of  its  body.  Besides,  the  breasts  of  aquatic  birds  are  ex- 
posed to  cold,  not  only  from  the  temperature  of  the  water,  but 
also  from  the  velocity  with  which  the  breast  of  the  bird  strikes 
against  it ;  and  likewise  from  the  rapid  evaporation  occasioned 
in  that  (Jart  by  the  air  against  which  it  strikes,  after  it  has  been 
moistened  by  dipping  from  time  to  time  into  the  water. 

If  you  hold  a  finger  of  one  hand  motionless  in  a  glass  of  wa- 
ter, and  at  the  same  time  move  a  finger  of  the  other  hand 
swiftly  through  water  of  the  same  temperature,  a  different 
sensation  will  be  soon  perceived  in  the  different  fingers.f 

Most  animal  substances,  especially  those  which  Providence 
has  assigned  as  a  covering  for  animals,  such  as  fur,  wool,  hair, 

*  One  reason  why  fur,  down,  &c.  conduct  heat  so  badly,  is,  that 
they  contain  a  targe  quantity  of  air,  which  is  a  worse  conductor  than 
the  materials  themselves.  G. 

t  f  he  reason  seems  to  be,  that  the  finger,  when  it  is  still,  warms  the 
water  in  contact  with  it :  while  the  one  that  is  stirring  is  constantly 
exposed  to  fresh  applications  of  cold.  C. 

5 


i&  FREE    CALORIC, 

skin,  &c.  are  bad.  conductors  of  heat,  and  are,  on  that  account, 
such  excellent  preservatives  against  the  inclemency  of  winter, 
that  our  warmest  apparel  is  made  of  these  materials. 

Emily.  Wood  is,  I  dare  say,  not  so  good  a  conductor  as  me- 
tal, and  it  is  for  that  reason,  no  doubt,  that  silver  tea-pots  have 
always  wooden  handles. 

Mrs.  ti.  Yes  ;  and  it  is  the  facility  with  which  metals  con- 
duct caloric  that  made  you  suppose  that  a  silver  pot  radiated 
more  caloric  than  an  earthen  one.  The  silver  pot  is  in  fact  hot- 
ter to  the  hand  when  in  contact  with  it ;  but  it  is  because  its 
conducting  power  more  than  counterbalances  its  deficiency  in 
regard  to  radiation. 

We  have  observed  that  the  most  dense  bodies  are  in  general 
the  best  conductors ;  and  metals,  you  know,  are  of  that  class. 
Porous  bodies,  such  as  the  earths  and  wood,  are  worse  conduct- 
ors, chiefly,  I  believe,  on  account  of  their  pores  being  filled 
with  air  ;  for  air  is  a  remarkably  bad  conductor. 

Caroline.  It  is  a  very  fortunate  circumstance  that  air  should 
be  a  bad  conductor,  as  it  tends  to  preserve  the  heat  of  the  body 
when  exposed  to  cold  weather. 

Mrs.  B.  It  is  one  of  the  many  benevolent  dispensations  of 
Providence,  in  order  to  soften  the  inclemency  of  the  seasons, 
and  to  render  almost  all  climates  habitable  to  man. 

In  fluids  of  different  densities,  the  power  of  conducting  heat 
varies  no  less  remarkably  ;  if  you  dip  your  hand  into  this  vessel 
full  of  mercury,  you  will  scarcely  conceive  that  its  temperature 
is  not  lower  than  that  of  the  atmosphere. 

Caroline.  Indeed  I  know  not  how  to  believe  it,  it  feels  so 
extremely  cold. — But  we  may  easily  ascertain  its  true  tempera- 
ture by  the  thermometer. — It  is  really  not  colder  than  the  air: 
— the  apparent  difference  then  is  produced  merely  by  the  differ- 
ence of  the  conducting  power  in  mercury  and  in  air. 

Mrs.  B.  Yes;  hence  you  may  judge  how  little  the  sense  of 
feeling" is  to  be  relied  on  as  a  test  of  the  temperature  of  bodies, 
and  how  necessary  a  thermometer  is  for  that  purpose. 

It  has  indeed  been  doubted  whether  fluids  have  the  power 
of  conducting  caloric  in  the  same  manner  as  solid  bodies. 
Count  Rumford,  a  very  few  years  since,  attempted  to  prove, 
by  a  variety  of  experiments,  that  fluids,  when  at  rest,  were 
not  at  all  endowed  fvith  this  property. 

Caroline.  How  is  that  possible,  since  they  are  capable  of 
imparting  cold  or  heat  to  us ;  for  if  they  did  not  conduct  heat, 
they  would  neither  take  it  from,  nor  give  it  to  us  ? 

ji.rs.  •.  .  Count  Rumford  did  not  mean  to  say  that  fluids 
would  not  communicate  their  heat  to  solid  bodies  j  but  only 


FREE    CALORIC.  3$ 

-/at  heat  does  not  pervade  fluids,  that  is  to  say,  is  not  transmit- 
ted from  one  particle  of  a  fluid  to  another,  in  the  same  manner. 
as  in  solid  bodies. 

Emily.  But  when  you  heat  a  vessel  of  water  over  the  fire,  it 
the  particles  of  water  do  not  communicate  heat  to  each  other^ 
how  does  the  water  become  hot  throughout  ? 

Mrs.  B.  By  constant  agitation.  Water,  as  you  have  seen, 
expands  by  heat  in  the  same  manner  as  solid  bodies  ;  the  heated 
particles  of  water,  therefore,  at  the  bottom  of  the  vessel,  be- 
come specifically  lighter  than  the  rest  of  the  liquid,  and  conse- 
quently ascend  to  the  surface,  where,  parting  with  some  of  their 
heat  to  the  colder  atmosphere,  they  are  condensed,  and  give 
way  to  a  fresh  succession  of  heated  particles  ascending  from 
the  bottom,  which  having  thrown  off  their  heat  at  the  surface,, 
are  in  their  turn  displaced.  Thus  every  particle  is  successively 
heated  at  the  bottom,  and  cooled  at  the  surface  of  the  liquid ; 
but  as  the  fire  communicates  heat  more  rapidly  than  the  atmos- 
phere cools  the  succession  of  surfaces,  the  whole  of  the  liquid 
in  time  becomes  heated. 

Caroline.  This  accounts  most  ingeniously  for  the  propaga- 
tion of  heat  upwards.  But  suppose  you  were  to  heat  the  up- 
per surface  of  a  liquid,  the  particles  being  specifically  lighter 
than  those  below,  could  not  descend  :  how  therefore  would  the 
heat  be  communicated  downwards? 

Mrs.  B.  If  there  were  no  agitation  to  force  the  heated  sur- 
face downwards,  Count  Rumford  assures  us  that  the  heat  would 
not  descend.  In  proof  of  this  he  succeeded  in  making  the  up- 
per surface  of  a  vessel  of  water  boil  and  evaporate,  while  a 
cake  of  ice  remained  frozen  at  the  bottom.* 

Caroline.  That  is  very  extraordinary  indeed  ! 

Mrs.  B.  It  appears  so,  because  we  are  not  accustomed  to 
heat  liquids  by  their  upper  surface ;  but  you  will  understand 
this  theory  better  if  I  show  you  the  internal  motion  that  takes 
place  in  liquids  when  they  experience  a  change  of  temperature. 
The  motion  of  the  liqnid  itself  is  indeed  invisible  from  the  ex- 
treme minuteness  of  its  particles ;  but  if  you  mix  with  it  any 
coloured  dust,  or  powder,  of  nearly  the  same  specific  gravity  as 
the  liquid,  you  may  judge  of  the  inteinal  motion  of  the  latter 
by  that  of  the  coloured  dust  it  contains. — Do  you  see  the  small 

*Dr.  Thomson  says — "  All  fluids,  however,  are  capable  of  conduct- 
ing caloric ;  for  when  the  source  of  heat  is  applied  to  their  surface, 
the  caloric  gradually  makes  its  way  downwards,  and  the  temperature 
of  every  stratum  gradually  diminishes  from  the  surface  to  the  bottom 
cf  the  liouid."  C, 


40  FUSE    CALORIC. 

piece  of  amber  moving  about  in  the  liquid  contained  in  this 
phial  ? 

Caroline.  Yes,  perfectly. 

Jl-rs.  B.  We  shall  now  immerse  the  phial  in  a  glass  of  hot 
water,  and  the  motion  of  the  liquid  will  be  shown  by  that  which 
it  communicates  to  the  amber. 

Emily.  I  see  two  currents,  the  one  rising  along  the  sides  of 
the  phial,  the  other  descending  in  the  centre  ;  but  I  do  not  un- 
derstand the  reason  of  this. 

Mrs.  B.  The  hot  water  communicates  its  caloric,  through  the 
medium  of  the  phial,  to  the  particles  of  the  fluid  nearest  to 
the  glass ;  these  dilate  and  ascend  laterally  to  the  surface, 
v  here,  in  parting  with  their  heat,  they  are  condensed,  and  in 
descending,  form  the  central  current. 

Caroline.  This  is  indeed  a  very  clear  and  satisfactory  exper- 
iment ;  but  how  much  slower  the  currents  now  move  than  they 
Uid  at  first  ? 

Mrs.  B.  It  is  because  the  circulation  of  particles  has  nearly 
produced  an  equilibrium  of  temperature  between  the  liquid  in 
the  glass  and  that  in  the  phial. 

Caroline.  But  these  communicate  laterally,  and  I  thought 
that  heat  in  liquids  could  be  propagated  only  upwards. 

Mrs.  B.  You  do  not  take  notice  that  the  heat  is  imparted 
from  one  liquid  to  the  other,  through  the  medium  of  the  phial 
itself,  the  external  surface  of  which  receives  the  heat  from  the 
water  in  the  glass,  whilst  its  internal  surface  transmits  it  to  the 
liquid  it  contains.  Now  take  the  phial  out  of  the  hot  water, 
and  observe  the  effect  of  its  cooling. 

Emily.  The  currents  are  reversed  ;  the  external  current  now 
descends,  and  the  internal  one  rises. — I  guess  the  reason  of 
this  change  : — the  phial  being  in  contact  with  cold  air  instead 
of  hot  water,  the  external  particles  are  cooled  instead  of  being 
heated  ;  they  therefore  descend  and  force  up  the  central  parti- 
cles; which,  being  warmer,  are  consequently  lighter. 

Mrs.  tt.  It  is  just  so.  Count  Rumford  hence  infers,  that  no 
alteration  of  temperature  can  take  place  in  a  fluid,  without  an 
internal  motion  of  its  particles  ;  and  as  this  motion  is  produced 
only  by  the  comparative  levity  of  the  heated  particles,  heat 
cannot  be  propagated  downwards. 

But  though  I  believe  that  Count  Rumford's  theory  as  to 
heat  being  incapable  of  pervading  fluids  is  not  strictly  cor- 
rect, yet  there  is,  no  doubt,  much  truth  in  li.s  observation, 
tha  the  communication  is  materially  promoted  by  a  motion 
of  the  parts  ;  and  this  accounts  for  the  cold  that  is  found  to 
prevail  at  the  bottom  of  the  lakes  in  Switzerland,  which  are 
fed  by  rivers  issuing  from  the  snowy  Alps,  The  water  of 


CALORIC.  41 

these  rivers  being  colder,  and  therefore  more  dense  than  that  of 
She  lakes,  subsides  to  the  bottom,  where  it  cannot  be  affected 
by  the  warmer  temperature  of  the  surface ;  the  motion  of  the 
waves  may  communicate  this  temperature  to  some  little  depth, 
but  it  can  descend  no  further  than  the  agitation  extends. 

Emily.  But  when  the  atmosphere  is  colder  than  the  lake,  the 
colder  surface  of  the  water  will  descend,  for  the  very  reason 
that  the  warmer  will  not. 

Mrs.  6.  Certainly  ;  and  it  is  on  this  account  that  neither  a 
lake,  nor  any  body  of  svater  whatever,  can  be  frozen  until  every 
particle  of  the  water  has  risen  to  the  surface  to  give  off  its  calo- 
ric to  the  colder  atmosphere ;  therefore  the  deeper  a  body  of 
water  is,  the  longer  will  be  the  time  it  requires  to  be  frozen. 

Emily.  But  if  the  temperature  of  the  whole  body  of  water 
be  brought  down  to  the  freezing  point,  why  is  only  the  surface 
frozen  ? 

Mrs.  B.  The  temperature  of  the  whole  body  is  lowered,  but 
not  to  the  freezing  point.  The  diminution  of  heat,  as  you 
know,  produces  a  contraction  in  the  bulk  of  fluids,  us  well  as 
of  solids.  This  effect,  however,  does  not  take  place  in  water 
below  the  temperature  of  40  degrees,  which  is  8  degrees  above 
the  freezing  point.  At  that  temperature,  therefore,  the  inter- 
nal motion,  occasioned  by  the  increased  specific  gravity  of  the 
condensed  particles,  ceases  ;  for  when  the  water  at  I  he  surface 
no  longer  condenses,  it  will  no  longer  descend,  and  leave  a 
fresh  surface  exposed  to  the  atmosphere  :  this  surface  alone, 
therefore,  will  be  further  exposed  to  its  severity,  and  will  soon 
be  brought  down  to  the  freezing  point,  when  it  becomes  ice? 
which  being  a  bad  conductor  of  heat,  preserves  the  water  be- 
neath a  long  time  from  being  affected  by  the  external  cold. 

Caroline.  And  the  sea  does  not  freeze,  I  suppose,  because 
its  depth  is  so  great,  that  a  frost  never  lasts  long  enough  to 
bring  down  the  temperature  of  such  a  great  body  of  water  to 
40  degrees  ? 

Jllrs.  H.  That  is  one  reason  why  the  sea,  as  a  large  mass  of 
water,  does  not  freeze.  But,  independently  of  this,  salt  water 
does  not  freeze  till  it  is  cooled  much  below  32  degrees,  and 
with  respect  to  the  law  of  condensation,  salt  water  is  an  ex- 
ception, as  it  condenses  even  many  degrees  below  the  freezing 
point.  When  the  caloric  of  fresh  water,  therefore,  is  impris- 
oned by  the  ice  on  its  surface,  the  ocean  still  continues  throw- 
ing offbeat  into  the  atmosphere,  which  is  a  most  signal  dispen- 
sation of  Providence  to  moderate  the  intensity  of  the  cold  in 
winter. 

Caroline.  This  theory  of  the  non-conducting  power  ef  & 


42  FREE  CALORIC. 

quids,  does  not,  I  suppose,  hold  good  with  respect  to  air, 
otherwise  the  atmosphere  would  not  be  heated  by  the  rays  of 
the  sun  passing  through  it  ? 

Mrs.  B.  Nor  is  it  heated  in  that  way.  The  pure  atmosphere 
is  a  perfectly  transparent  medium,  which  neither  radiates,  ab- 
sorbs, nor  conducts  caloric,  but  transmits  the  rays  of  the  sun 
to  us  without  in  any  way  diminishing  their  intensity.  The  air 
is  therefore  not  more  heated,  by  the  sun's  rays  passing  through 
it,  than  diamond,  glass,  water,  or  any  other  transparent  me- 
dium.* 

Caroline.  That  is  very  extraordinary  !  Are  glass  windows 
not  heated  then  by  the  sun  shining  on  them  ? 

Mrs.  B.  No;  not  if  the  glass  be  perfectly  transparent.  A 
most  convincing  proof  that  glass  transmits  the  rays  of  the  sun 
without  being  heated  by  them  is  afforded  by  the  burning  lens, 
which  by  converging  the  rays  to  a  focus  will  set  combustible 
bodies  on  fire,  without  its  own  temperature  being  raised. 

Emily.  Yet,  Mrs.  B.,  if  I  hold  a  piece  of  glass  near  the  fire, 
it  is  almost  immediately  warmed  by  it ;  the  glass  therefore  must 
retain  some  of  the  caloric  radiated  by  the  fire  ?  Is  it  that  the 
solar  rays  alone  pass  freely  through  glass  without  paying  trib- 
ute? It  seems  unaccountable  that  the  radiation  of  a  common 
fire  should  have  power  to  do  what  the  sun's  rays  cannot  accom- 
plish. 

Mrs.  B.  It  is  not  because  the  rays  from  the  fire  have  more 
power,  but  rather  because  they  have  less,  that  they  heat  glass 
and  other  transparent  bodies.  It  is  true,  however,  that  as  you 
approach  the  source  of  heat  the  rays  being  nearer  each  other, 
the  heat  is  more  condensed,  and  can  produce  effects  of  which 
the  solar  rays,  from  the  great  distance  of  their  source,  are  inca- 
pable. Thus  we  should  find  it  impossible  to  roast  a  joint  of 
m-^at  by  the  sun's  rays,  though  it  is  so  easily  done  by  culinary 
h«  at.  Yet  calorie  emanated  from  burning  bodies,  which  is 
commonly  called  culinary  heat,  has  neither  the  intensity  nor  the 
velocity  of  solar  rays.  All  caloric,  we  have  said,  is  supposed 
to  proceed  originally  from  the  sun;  but  after  having  been  incor- 
porated with  terrestrial  bodies,  and  again  given  out  by  them, 
though  its  nature  is  not  ess«  nfially  altered,  it  retains  neither  the 
intensity  nor  the  velocity  with  which  it  first  emanated  from 
that  luminary;  it  has  therefore  not  the  power  of  passing  through 

*  To  show  still  better  that  transparent  media  are  not  heated  by  the 
»ays  of  the  sun,  throw  the  focus  of  a  hurnine;  lens  into  a  vessel  of  clear 
water.  ISo  effect  on  the  temperature  will  be  produced;  but  if  an 
spake  body,  as  a  piece  of  cork  be  introduced  under  the  focus,  the  nra- 
ter  at  this  point  instantly  begins  to  boih  C. 


CALORIC.  43 

transparent  mediums,  such  as  glass  and  water,  without  being 
partially  retained  by  those  bodies. 

Emily.  I  recollect  that  in  the  experiment  on  the  reflection  of 
heat,  the  glass  skreen  which  you  interposed  between  the  burn- 
ing taper  and  the  mirror,  arrested  the  rays  of  caloric,  and  suf- 
fered only  those  of  light  to  pass  through  it. 

Caroline.  Glass  windows,  then,  though  they  cannot  be  heat- 
ed by  the  sun  shining  on  them,  may  be  heated  internally  by  a 
fire  in  the  room  ?  But,  Mrs.  B.,  since  the  atmosphere  is  not 
warmed  by  the  solar  rays  passing  through  it,  how  does  it  obtain 
heat ;  for  all  the  fires  that  are  burning  on  the  surface  of  the 
earth  would  contribute  very  little  towards  warming  it  ? 

Emily.  The  radiation  of  heat  is  not  confined  to  burning  bod- 
ies ;  for  all  bodies,  you  know,  have  that  property ;  therefore 
not  only  every  thing  upon  the  surface  of  the  earth,  but  the 
earth  itself,  must  radiate  heat ;  and  this  terrestrial  caloric,  not 
having,  I  suppose,  sufficient  power  to  traverse  the  atmosphere, 
communicates  heat  to  it. 

Mrs.  13.  Your  inference  is  extremely  well  drawn,  Emily  ; 
but  the  foundation  on  which  it  rests  is  not  sound  :  for  the  fact 
is,  that  terrestrial  or  culinary  heat,  though  it  cannot  pass  through 
the  denser  transparent  mediums,  such  as  glass  or  water,  without 
loss,  traverses  the  atmosphere  completely  ;  so  that  all  the  heat 
which  the  earth  radiates,  unless  it  meet  with  clouds*  or  any 
foreign  body  to  intercept  its  passage,  passes  into  the  distant  re- 
gions of  the  universe. 

Caroline.  What  a  pity  that  so  much  heat  should  be  wasted ! 

Mrs.  B.  Before  you  are  tempted  to  object  to  any  law  of  na- 
ture, reflect  whether  it  may  not  prove  to  be  one  of  the  number- 
less dispensations  of  Piovidence  for  our  good.  If  all  the  heat 
which  the  earth  has  received  from  the  sun,  since  the  creation 
hud  been  accumulated  in  it,  its  temperature  by  this  time  would, 
no  doubt,  have  been  more  elevated  than  any  human  being  could 
have  borne. 

Caroline.  I  spoke  indeed  very  inconsiderately.  But,  Mrs. 
B  ,  though  the  earth,  at  such  a  high  temperature,  might  have 
scorched  our  feet,  we  should  always  have  had  a  cool  refreshing 
air  to  breathe,  since  the  radiation  of  the  earth  does  not  heat  the 
atmosphere. 

Emily.  The  cool  air  would  have  afforded  but  very  insufficient 

*  Every  one  has  observed  how  oppressive  the  heat  is  on  a  foggy,  o? 
cloudy  day  in  the  summer.  The  moisture  of  the  f')g  absorbs  the  heat- 
which  the  earth  radiates,  and  throws  it  back, upon  the  earth  again, 
and  upon  us.  C, 


44  FREE   CALORIC, 

Jrefreshnaent,  whilst  our  bodies  were  exposed  to  the  burning  fa* 
diation  of  the  earth. 

Mrs.  B.  Nor  should  we  have  breathed  a  cool  air ;  for  though 
it  is  true  that  heat  is  not  communicated  to  the  atmosphere  by 
radiation,  yet  the  air  is  warmed  by  contact  with  heated  bodies, 
in  the  same  manner  as  solids  or  liquids.  The  stratum  of  air 
which  is  immediately  in  contact  with  the  earth  is  heated  by  it ; 
it  becomes  specifically  lighter  and  rises,  making  way  for  another 
stratum  of  air  which  is  in  its  turn  heated  and  carried  upwards  ; 
and  thus  each  successive  stratum  of  air  is  warmed  by  coming  in 
contact  with  the  earth.  You  may  perceive  this  effect  in  a  sultry 
day,  if  you  attentively  observe  the  strata  of  air  near  the  surface 
of  the  earth;  they  appear  in  constant  agitation,  for  though  it  is 
true  the  air  is  itself  invisible,  yet  the  sun  shining  on  the  vapours 
floating  in  it,  render  them  visible,  like  the  amber  dust  in  the  wa- 
ter. The  temperature  of  the  surface  of  the  earth  is  therefore  the 
source  from  whence  the  atmosphere  derives  its  heat,  though  it 
is  communicated  neither  by  radiation,  nor  transmitted  from  one 
particle  of  it  to  another  by  the  conducting  power  ;  but  every 
particle  of  air  must  come  in  contact  with  the  earth  in  order  to 
receive  heat  from  it. 

Emily.  Wind  then  by  agitating  the  air  should  contribute  to 
cool  the  earth  and  warm  the  atmosphere,  by  bringing  a  more 
rapid  succession  of  fresh  strata  of  air  in  contact  with  the  earth, 
and  yet  in  general  wind  feels  cooler  than  still  air? 

Mrs.  B.  Because  the  agitation  of  the  air  carries  off  heat 
from  the  surface  of  our  bodies  more  rapidly  than  still  air,  by 
occasioning  a  greater  number  of  points  of  contact  in  a  given 
time. 

Emily.  Since  it  is  from  the  earth  and  not  the  sun  that  the  at- 
mosphere receives  its  heat,  I  no  longer  wonder  that  elevated 
regions  should  be  colder  than  plains  and  valleys ;  it  was  always 
a  subject  of  astonishment  to  me,  that  in  ascending  a  mountain 
and  approaching  the  sun,  the  air  became  colder  instead  of  being 
more  heated. 

Mrs.  B.  At  the  distance  of  about  a  hundred  million  of  miles, 
which  we  are  from  the  sun,  the  approach  of  a  few  thousand  feel 
makes  no  sensible  difference,  whilst  it  produces  a  very  consid- 
erable effect  with  regard  to  the  warming  the  atmosphere  at  the 
surface  of  the  earth. 

Caroline.  Yet  as  the  warm  air  arises  from  the  earth  and  the 
cold  air  descends  to  it,  I  should  have  supposed  that  heat  would 
have  accumulated  in  the  upper  regions  of  the  atmosphere,  and 
that  we  should  have  felt  the  air  warmer  as  we  ascended  ? 

Mrs.  j?.  The  atmosphere,  you  know,  diminishes  in  density. 


II 


*i 


II-S 


FREE  CALORIC.  43 

und  consequently  in  weight,  as  it  is  more  distant  from  the  earth  ; 
the  warm  air,  therefore,  rises  till  it  meets  with  a  stratum  of  air 
of  its  own  density  ;  and  it  will  not  ascend  into  the  upper  regions 
of  the  atmosphere  until  all  the  parts  beneath  have  been  previ- 
ously heated.  The  length  of  summer  even  in  warm  climates 
does  not  heat  the  air  sufficiently  to  melt  the  snow  which  has  ac- 
cumulated during  the  winter  on  very  high  mountains,  although 
they  are  almost  constantly  exposed  to  the  heat  of  the  sun's  rays, 
being  too  much  elevated  to  be  often  enveloped  in  clouds. 

Emily.  These  explanations  are  very  satisfactory  ;  but  allow 
me  to  ask  you  one  more  question  respecting  the  increased  levity 
of  heated  liquids.  You  said  that  when  water  was  heated  over 
the  fire,  the  particles  at  the  bottom  of  the  vessel  ascended  as 
soon  as  heated,  in  consequence  of  their  specific  levity  :  why- 
does  not  the  same  effect  continue  when  the  water  boils,  and  is 
converted  into  steam  ?  and  why  does  the  steam  rise  from  the 
surface,  instead  of  the  bottom  of  the  liquid  ? 

Mrs.  B.  The  steam  or  vapour  does  ascend  from  the  bottom, 
though  it  seems  to  arise  from  the  surface  of  the  liquid.  We 
shall  boil  some  water  in  this  Florence  flask,  (PLATE  IV.  Fig. 
1.)  in  order  that  you  may  be  well  acquainted  with  the  process 
of  ebullition  ; — you  will  then  see,  through  the  glass,  that  the 
vapour  rises  in  bubbles  from  the  bottom.  We  shall  make  it 
boil  by  means  of  a  lamp,  which  is  more  convenient  for  this 
purpose  than  the  chimney  fire. 

Emily.  I  see  some  small  bubbles  ascend,  and  a  great  many 
appear  all  over  the  inside  of  the  flask ;  does  the  water  begin  to 
boil  already  ? 

Mrs.  B.  No ;  what  you  now  see  are  bubbles  of  air,  which 
were  either  dissolved  in  the  water,  or  attached  to  the  inner  sur- 
face of  the  flask,  and  which,  being  rarefied  by  the  heat,  ascend 
in  the  water. 

Emily.  But  the  heat  which  rarefies  the  air  inclosed  in  the 
water  must  rarefy  the  water  at  the  same  time;  therefore,  if  it 
could  remain  stationary  in  the  water  when  both  were  cold,  I  do 
not  understand  why  it  should  not  when  both  are  equally 
heated  ? 

Mrs.  B.  Air  being  much  less  dense  than  water,  is  more  easily 
ram  lormer,  therefore,  expands  to  a  great  extent, 

whilstWe  latter  continues  to  occupy  nearly  the  same  space  ; 
for  water  dilates  comparatively  but  very  little  without  changing 
its  state  and  becoming  vapour.  Now  that  the  water  in  the  flask 
begins  to  boil,  observe  what  large  bubbles  rise  from  the  bottom 
of  it. 

Emily.  I  see  them  perfectly  ;  but  I  wonder  that  they  have 
sufficient  power  to  force  themselves  through  the  water, 


46  FREE    CALORIC. 

Caroline.  They  must  rise,  you  know,  from  their  specific  lev- 
ity. 

Mrs.  B.  You  are  right,  Caroline ;  but  vapour  has  not  in  all 
liquids  (when  brought  to  the  degree  of  vaporization)  the  power 
of  overcoming  the  pressure  of  the  less  heated  surface.  Metals, 
for  instance,  mercury  excepted,  evaporate  only  from  the  sur- 
face ;  therefore  no  vapour  will  ascend  from  them  till  the  degree 
of  heat  which  is  necessary  to  form  it  has  reached  the  surface; 
that  is  to  say,  till  the  whole  of  the  liquid  is  brought  to  a  state  of 
ebullition. 

Emily.  I  have  observed  that  steam,  immediately  issuing 
from  the  spout  of  a  tea-kettle,  is  less  visible  than  at  a  further 
distance  from  it ;  yet  it  must  be  more  dense  when  it  first  evap- 
orates, than  when  it  first  begins  to  diffuse  itself  in  the  air. 

Mrs.  />;.  When  the  steam  is  first  formed,  it  is  so  perfectly 
dissolved  by  caloric,  as  to  be  invisible.  In  order  however  to 
understand  this,  it  will  be  necessary  for  me  to  enter  into  some 
explanation  respecting  the  nature  of  SOLUTION.  Solution  takes 
place  whenever  a  body  is  melted  in  a  fluid.  In  this  operation 
the  body  is  reduced  to  such  a  minute  state  of  division  by  the  flu- 
id, as  to  become  invisible  in  it,  and  to  partake  of  its  fluidity  ; 
but  in  common  solutions  this  happens  without  any  decomposi- 
tion, the  body  being  only  divided  into  its  integrant  particles  by 
the  fluid  in  which  it  is  melted. 

Caroline.  It  is  then  a  mode  of  destroying  the  attraction  of 
aggregation. 

Mrs.  B.  Undoubtedly. — The  two  principal  solvent  fluids 
are  water  and  caloric.  You  may  have  observed  that  if  you 
melt  salt  in  water  it  totally  disappears,  and  the  water  remains 
clear,  and  transparent  as  before  ;  yet  though  the  union  of  these 
two  bodies  appears  so  perfect,  it  is  not  produced  by  any  chem- 
ical combination  ;  both  the  salt  and  the  water  remain  unchang- 
ed ;  and  if  you  were  to  separate  them  by  evaporating  the  latter, 
you  would  find  the  salt  in  the  same  state  as  before. 

Emily.  I  suppose  that  water  is  a  solvent  for  solid  bodies, 
and  caloric  for  liquids  ? 

Mrs.  B.  Liquids  of  course  can  only  be  converted  into  vapour 
by  caloric.  But  the  solvent  power  of  this  agent  is  not  at  all 
confined  to  that  class  of  bodies ;  a  great  variety  ofjgo^d  sub- 
stances are  dissolved  by  heat :  thus  metals,  which  aMBnsolu- 
ble  in  water,  can  be  dissolved  by  intense  heat,  being  first  fused 
or  converted  into  a  liquid,  and  then  rarefied  into  an  invisible 
vapour.  Many  other  bodies,  such  as  salt,  gums,  &c.  yield  to 
<-hher  of  these  solvents. 


FREE    CALORIC.  47 

Caroline.  And  that,  no  doubt,  is  the  reason  why  hot  water 
will  melt  them  so  much  better  than  cold  water? 

Mrs.  B.  It  is  so.  Caloric  may,  indeed,  be  considered  as 
having,  in  every  instance,  some  share  in  the  solution  of  a  body 
by  water,  since  water,  however  low  its  temperature  may  be, 
always  contains  more  or  less  caloric. 

Emily.  Then,  perhaps,  water  owes  its  solvent  power  merely 
to  the  caloric  contained  in  it. 

Mrs.  B.  That,  probably,  would  be  carrying  the  speculation 
too  far;  I  should  rather  think  that  water  and  caloric  unite  their 
efforts  to  dissolve  a  body,  and  that  the  difficulty  or  facility  of 
effecting  this,  depend  both  on  the  degree  of  attraction  of  ag- 
gregation to  be  overcome,  and  on  the  arrangement  of  the  par- 
ticles which  are  more  or  less  disposed  to  be  divided  and  pene- 
trated by  the  solvent. 

Emily.  But  have  not  all  liquids  the  same  solvent  power  as 
water  ? 

Mrs.  B.  The  solvent  power  of  other  liquids  varies  according 
to  their  nature,  and  that  of  the  substances  submitted  to  their 
action.  Most  of  these  solvents,  indeed,  differ  essentially  from 
water,  as  they  do  not  merely  separate  the  integrant  particles  of 
the  bodies  which  they  dissolve,  but  attack  their  constituent 
principles  by  the  power  of  chemical  attraction,  thus  producing 
a  true  decomposition.  These  more  complicated  operations  we 
must  consider  in  another  place,  and  confine  our  attention  at 
present  to  the  solutions  by  water  and  caloric. 

Caroline.  But  there  are  a  variety  of  substances  which,  when 
dissolved  in  water,  make  it  thick  and  muddy,  and  destroy  its 
transparency. 

Mrs.  B.  "in  this  case  it  is  not  a  solution,  but  simply  a  mix- 
ture. I  shall  show  you  the  difference  between  a  solution  and  a 
mixture,  by  putting  some  common  salt  into  one  glass  of  water, 
and  some  powder  of  chalk  into  another ;  both  these  substances 
are  white,  but  their  effect  on  the  water  will  be  very  different. 

Caroline.  Very  different  indeed  !  The  salt  entirely  disap- 
pears and  leaves  the  water  transparent,  whilst  the  chalk  chan- 
ges it  into  an  opaque  liquid  like  milk. 

Emily.  And  would  lumps  of  chalk  and  salt  produce  similar 
effects  on  water  ? 

Mrs.  B.  Yes,  but  not  so  rapidly :  salt  is,  indeed,  soon  melted 
though  in  a  lump  ;  but  chalk,  which  does  not  mix  so  readily 
with  water,  would  require  a  much  greater  length  of  time ;  I 
therefore  preferred  showing  you  the  experiment  with  both  sub- 
stances reduced  to  powder,  which  does  not,  in  any  respect  alter 


48  FREE    CALORIC. 

their  nature,  but  facilitates  the  operation  merely  by  presenting 
a  greater  quantity  of  surface  to  the  water. 

I  must  not  forget  to  mention  a  veiy  curious  circumstance 
respecting  solutions,  which  is,  that  a  fluid  is  not  nearly  so 
much  increased  in  bulk  by  holding  a  body  in  solution,  as  it 
would  by  mere  mixture  with  the  body. 

Caroline.  That  seems  impossible;  for  two  bodies  cannot 
exist  together  in  the  same  space. 

Mrs.  B.  Two  bodies  may,  by  condensation,  occupy  less 
?pace  when  in  union  than  when  separate,  and  this  I  can  show 
you  by  an  easy  experiment. 

This  phial,  which  contains  some  salt,  I  shall  fill  with  water, 
pouring  it  in  quickly,  so  as  not  to  dissolve  much  of  the  salt ; 
and  when  it  is  quite  full  I  cork  it. — If  I  now  shake  the  phial 
till  the  salt  is  dissolved,  you  will  observe  that  it  is  no  longer 
full. 

Caroline.  I  shall  try  to  add  a  little  more  salt. — But  now,  you 
see,  Mrs.  B.,  the  water  runs  over. 

Airs.  B.  Yes  ;  but  observe  that  the  last  quantity  of  salt  you 
put  in  remains  solid  at  the  bottom,  and  displaces  the  water; 
for  it  has  already  melted  all  the  salt  it  is  capable  of  holding  in 
solution.  This  is  called  the  point  of  saturation;  and  the  wa- 
ter in  this  case  is  said  to  be  saturated  with  salt. 

Emily.  I  think  I  now  understand  the  solution  of  a  solid  body 
by  water  perfectly ;  but  I  have  not  so  clear  an  idea  of  the  solu- 
tion of  a  liquid  by  caloric. 

Mrs.  B.  It  is  probably  of  a  similar  nature ;  but  as  caloric  is 
an  invisible  fluid,  its  action  as  a  solvent  is  not  so  obvious  as  that 
of  water.  Caloric,  we  may  conceive,  dissolves  water,  and  con- 
verts it  into  vapour  by  the  same  process  as  water  dissolves  salt- 
that  is  to  say,  the  particles  of  water  are  so  minutely  divided  by 
the  caloric  as  to  become  invisible.  Thus,  you  are  now  enabled 
to  understand  why  the  vapour  of  boiling  water,  when  it  first  is- 
sues from  the  spout  of  a  kettle,  is  invisible;  it  is  so,  because  it 
is  then  completely  dissolved  by  caloric.  But  the  air  wifh  which 
it  comes  in  contact,  being  much  colder  than  the  vapour,  the 
latter  yields  to  it  a  quantity  of  its  caloric.  The  particles  of  va- 
pour being  thus  in  a  great  measure  deprived  of  their  solvent, 
gradually  collect,  and  become  visible  in  the  form  of  stenro,  whi  h 
is  water  in  a  state  of  imperfect  solution;  and  if  you  were  I'ur- 
ther  to  deprive  it  of  its  caloric,  it  would  return  to  its  original  li- 
quid state. 

Caroline.  That  I  understand  very  well.  If  you  hold  a  cold 
plate  ov^r  a  tea-urn,  the  steam  issuing  from  it  will  be  immedi- 
ately converted  into  drops  of  water  by  parting  with  its  calorir 


FREE    CALORIC.  4$ 

to  the  plate  5  but  in  what  state  is  the  steam,  when  it  becomes 
invisible  by  being  diffused  in  the  air  ? 

Mrs.  B.  It  is  not  merely  diffused,  but  is  again  dissolved  by 
the  air. 

Emily.  The  air,  then,  has  a  solvent  power,  like  water  and 
caloric  ? 

Mrs.  B.  This  was  formerly  believed  to  be  the  case.  But  it 
appears  from  more  recent  enquiries  that  the  solvent  power  of 
the  atmosphere  depends  solely  upon  the  caloric  contained  in  it. 
Sometimes  the  watery  vapour  diffused  in  the  atmosphere  is  but 
imperfectly  dissolved,  as  is  the  case  in  the  formation  of  clouds 
and  fogs  ;"  but  if  it  gets  into  a  region  sufficiently  warm,  it  be- 
comes perfectly  invisible. 

Emily.  Can  any  water  dissolve  in  the  atmosphere  without 
its  being  previously  converted  into  vapour  by  boiling  ? 

Mrs.  B.  Unquestionably ;  and  this  constitutes  the  difference 
between  vaporization  and  evaporation.  Water,  when  heated 
to  the  boiling  point,  can  no  longer  exist  in  the  form  of  water, 
and  must  necessarily  be  converted  into  vapour  or  steam,  what- 
ever may  be  the  state  and  temperature  of  the  surrounding  me- 
dium; this  is  called  vaporization.  But  the  atmosphere,  by 
means  of  the  caloric  it  contains,  can  take  up  a  certain  portion  of 
water  at  any  temperature,  and  hold  it  in  a  state  of  solution. 
This  is  simply  evaporation.  Thus  the  atmosphere  is  contin- 
ually carrying  off  moisture  from  the  surface  of  the  earth,  until 
it  is  saturated  with  it. 

Caroline.  That  is  the  case,  no  doubt,  when  we  feel  the  ati 
mosphere  damp 

Mrs.  B.  On  the  contrary,  when  the  moisture  is  well  dissol- 
ved it  occasions  no  humidity  :  it  is  only  when  in  a  state  of  im- 
perfect solution  and  floating  in  the  atmosphere,  in  the  form  of 
watery  vapour,  that  it  produces  dampness.  This  happens 
more  frequently  in  winter  than  in  summer ;  for  the  lower  the 
temperature  of  the  atmosphere,  the  less  water  it  can  dissolve ; 
and  in  reality  it  never  contains  so  much  moisture  as  in  a  dry 
hot  summer's  day. 

Caroline.  You  astonish  me  !  But  why,  then,  is  the  air  so  dry 
in  frosty  weather,  when  its  temperature  is  at  the  lowest  ? 

Emily.  This,  I  conjecture,  proceeds  not  so  much  from  the 
moisture  being  dissolved,  as  from  its  being  frozen  j*  is  not  that 
the  case  ? 

*  [n  cold  climates,  when  there  is  not  a  cloud  to  be  seen,  and  the  sun 
rises  in  all  his  glory,  the  air  is  sometimes  full  of  little  particles  of  ice* 
glistening  in  every'direction,  and  forming  a  most  beautiful  spectacle. 
This  is  owing  to  the  condensation,  and  freezing  of  the  pai  tides  of  wav 
ter  iqt  the  air,  by  the  intense  cold.  C. 

6 


50  FREE   CALORIC. 

Mrs.  B.  It  is ;  and  the  freezing  of  the  watery  vapour  which 
the  atmospheric  heat  could  not  dissolve,  produces  what  is  call- 
ed a  hoar  frost ;  for  the  particles  descend  in  freezing,  and  attach 
themselves  to  whatever  they  meet  with  on  the  surface  of  the 
earth. 

The  tendency  of  free  caloric  to  an  equilibrium,  together  with 
its  solvent  power,  are  likewise  connected  the  phenomena  of  rain, 
of  dew,  &c.  When  moist  air  of  a  certain  temperature  hap- 
pens to  pass  through  a  colder  region  of  the  atmosphere,  it  parts 
with  a  portion  of  its  heat  to  the  surrounding  air ;  the  quantity 
of  caloric,  therefore,  which  served  to  keep  the  water  in  a  state 
of  vapour,  being  diminished,  the  watery  particles  approach 
each  other,  and  form  themselves  into  drops  of  water,  which  be- 
ing heavier  than  the  atmosphere,  descend  to  the  earth.  There 
are  also  other  circumstances,  and  particularly  the  variation  in 
the  weight  of  the  atmosphere,  which  may  contribute  to  the  for- 
mation of  rain.  This,  however,  is  an  intricate  subject,  into 
which  we  cannot  more  fully  enter  at  present. 

Emily.  In  what  manner  do  you  account  for  the  formation  of 
dew  ? 

Mrs.  B.  Dew  is  a  deposition  of  watery  particles  or  minute 
drops  from  the  atmosphere,  precipitated  by  the  coolness  of 
the  evening. 

Caroline.  This  precipitation  is  owing,  I  suppose,  to  the  cool- 
ing of  the  atmosphere,  which  prevents  its  retaining  so  great  a 
quantity  of  watery  vapour  in  solution  as  during  the  heat  of 
the  day. 

Mrs.  B.  Such  was,  from  time  immemorial,  the  generally  re- 
ceived opinion  respecting  the  cause  of  dew ;  but  it  has  been 
very  recently  proved  by  a  course  of  ingenious  experiments  of 
Dr.  Wells,  that  the  deposition  of  dew  is  produced  by  the  cool- 
ing of  the  surface  of  the  earth,  which  he  has  shown  to  take 
place  previously  to  the  cooling  of  the  atmosphere  5  for  on  ex- 
amining the  temperature  of  a  plot  of  grass  just  before  the  dew- 
fall,  he  found  that  it  was  consideiably  colder  than  the  air  a  few 
feet  above  it,  from  whieh  the  dew  was  shortly  after  precipitated. 

Emily.  But  why  should  the  earth  cool  in  the  evening  sooner 
than  the  atmosphere  ? 

Mrs.  B.  Because  it  parts  with  its  heat  more  readily  than  the 
air ;  the  earth  is  an  excellent  radiator  of  caloric,  whilst  the  at- 
mosphere does  not  possess  that  property,  at  least  in  any  sensi- 
ble degree.  Towards  evening,  therefore,  when  the  solar  heat 
declines,  and  when  after  sunset  it  entirely  ceases,  the  earth 
rapidly  cools  by  radiating  heat  towards  the  skies ;  whilst  the 
air  has  no  means  of  parting  with  its  heat  but  by  corning  into 


FREE    CALORIC.  £>1 

contact  with  ihe  cooled  surface  of  the  earth,  to  which  it  com- 
municates its  caloric.  Its  solvent  power  being  thus  reduced, 
it  is  unable  to  retain  so  large  a  portion  of  watery  vapour,  and 
Deposits  those  pearly  drops  which  we  call  dew. 

Emily.  If  this  be  the  cause  of  dew,  we  need  not  be  appre- 
hensive of  receiving  any  injury  from  it ;  for  it  can  be  deposi- 
ted only  on  surfaces  that  are  colder  than  the  atmosphere,  which 
is  never  the  case  with  our  bodies. 

Mrs.  B.  Very  true ;  yet  I  would  not  advise  you  for  this  rea- 
son to  be  too  confident  of  escaping  all  the  ill  effects  which  may 
arise  from  exposure  to  the  dew  ;  for  it  may  be  deposited  on 
your  clothes,  and  chill  you  afterwards  by  its  evaporation  from 
them.  Besides,  whenever  the  dew  is  copious,  there  is  a  chill  in 
the  atmosphere  which  it  is  not  always  safe  to  encounter. 

Caroline.  Wind,  then,  must  promote  the  deposition  of  dew, 
by  bringing  a  more  rapid  succession  of  particles  of  air  in  con- 
tact with  the  earth,  just  as  it  promotes  the  cooling  of  the  earth 
and  warming  of  the  atmosphere  during  the  heat  of  the  day  ? 

Mrs.  B.  Yes ;  provided  the  wind  be  unattended  with  clouds, 
for  these  accumulations  of  moisture  not  only  prevent  the  free 
radiation  of  the  earth  towards  the  upper  regions,  but  themselves 
radiate  towards  the  earth;  under  these  circumstances  much 
less  dew  is  formed  than  on  fine  clear  nights,  when  the  radiation 
of  the  earth  passes  without  obstacle  through  the  atmosphere  to 
the  distant  regions  of  space,  whence  it  receives  no  caloric  in 
exchange.  The  dew  continuesto  be  deposited  during  the  night, 
and  is  generally  most  abundant  towards  morning;  when  the 
contrast  between  the  temperature  of  the  earth  and  that  of  the 
air  is|  greatest.  After  sunrise  the  equilibrium  of  temperature 
between  these  two  bodies  is  gradually  restored  by  the  solar 
rays  passing  freely  through  the  atmosphere  to  the  earth  ;  and 
later  in  the  morning  the  temperature  of  the  earth  gains  the  as- 
cendency, and  gives  out  caloric  to  the  air  by  contact,  in  the  same 
manner  as  it  receives  it  from  the  air  during  the  night. 

Can  you  tell  me,  now,  why  a  bottle  of  wine  taken  fresh  from 
the  cellar  (in  summer  particularly,)  will  soon   be  covered  with 
dew  ;  and  even  the  glasses  into  which  the  wine  is  poured  will 
•be  moistened  with  a  similar  vapour? 

Emily.  The  bottle  being  colder  than  the  surrounding  air, 
must  absorb  caloric  from  it;  the  moisture  therefore  which  that 
air  contained  becomes  visible,  and  forms  the  dew  which  is  de- 
posited on  the  bottle. 

.<7rs.  •'?.  Very  well,  Emily.  Now,  Caroline,  can  you  inform 
me  why,  in  a  warm  room,  or  close  carriage,  the  contrary  effect 


52  FREE    CALORIC. 

takes  place  ;  that  is  to  say,  that  the  inside  of  the  windows  it- 
covered  with  vapour  ? 

Caroline.  I  have  heard  that  it  proceeds  from  the  breath  oi 
those  within  the  room  or  the  carriage ;  and  I  suppose  it  is  occa- 
sioned by  the  windows  which,  being  colder  than  the  breath,  de- 
prive it  of  part  of  its  caloric,  and  by  this  means  convert  it  into 
watery  vapour. 

Mrs,  B.  You  have  both  explained  it  extremely  well.  Bod- 
ies attract  dew  in  proportion  as  they  are  good  radiators  of  ca- 
loric, as  it  is  this  quality  which  reduces  their  temperature  be- 
Jow  that  of  the  atmosphere;  hence  we  find  that  little  or  no  dew 
is  deposited  on  rocks5  sand,  water;  while  grass  and  living  veg- 
etables, to  which  it  is  so  highly  beneficial,  attract  it  in  abund- 
ance— another  remarkable  instance  of  the  wise  and  bountiful 
dispensations  of  Providence. 

Emily.  And  we  may  again  observe  it  in  the  abundance  of 
dew  in  summer,  and  in  hot  climates,  when  its  cooling  effects  are 
so  much  required;  but  I  do  not  understand  what  natural  cause 
increases  the  dew  in  hot  weather  ? 

Mrs.  B.  The  more  caloric  the  earth  receives  during  the  day. 
the  more  it  will  radiate  afterwards,  and  consequently  the  more 
rapidly  its  temperature  will  be  reduced  in  the  evening,  in  com- 
parison to  that  of  the  atmosphere.  In  the  West  Indies  espe- 
cially, where  the  intense  heat  of  the  day  is  strongly  contrasted 
with  the  coolness  of  the  evening,  the  dew  is  prodigiously  abun- 
dant. During  a  drought,  the  dew  is  less  plentiful,  as  the  earth 
is  not  sufficiently  supplied  with  moisture  to  be  able  to  saturate 
the  atmosphere. 

Caroline.  I  have  often  observed,  Mrs.  B.,  that  when  I  walk 
out  in  frosty  weather,  with  a  veil  over  my  face,  my  breath  free- 
zes upon  it.  Pray  what  is  the  reason  of  that  ? 

Jkrs.  B.  It  is  because  the  cold  air  immediately  seizes  on  the 
caloric  of  your  breath,  and  by  robbing  it  of  its  solvent,  reduces 
it  to  a  denser  fluid,  which  is  the  watery  vapour  that  settles  on 
your  veil,  and  there  it  continues  parting  with  its  caloric  till  it  is 
brought  down  to  the  temperature  of  the  atmosphere,  and  as- 
sumes the  form  of  ice. 

You  may,  perhaps,  have  observed  that  the  breath  of  animals, 
or  rather  the  moisture  contained  in  it,  is  visible  in  damp  weath- 
er, or  during  a  frost.  In  the  former  case,  the  atmosphere  being 
over-saturated  with  moisture,  can  dissolve  no  more.  In  the  lat- 
ter, the  cold  condenses  it  into  visible  vapour;  and  for  the  same 
reason,  the  steam  arising  from  water  that  is  warmer  than  the  at- 
mosphere, becomes  visible.  Have  you  never  taken  notice  of 


CALORIC.  53 

the  valour  rising  from  your  hands  after  having  dipped  them 
into  warm  water  ? 

Caroline.  Frequently,  especially  in  frosty  weather. 

A'irs.  <.  We  have  already  observed  that  pressure  is  an  ob- 
stacle to  evaporation  :  there  are  liquids  which  contain  so  great 
a  quantity  of  caloric,  and  whose  particles  consequently  auhei'e 
so  slightly  together,  that  they  may  be  rapidly  converted  into  va- 
pour without  any  elevation  of  temperature,  merely  by  taking  off 
the  weight  of  the  atmosphere.  In  such  liquids,  you  perceive, 
it  is  the  pressure  of  the  atmosphere  alone  that  connects  their 
particles,  and  keeps  them  in  a  liquid  stale. 

Caroline.  I  do  not  well  understand  why  the  particles  of 
such  fluids  should  be  disunited  and  converted  into  vapour,  with- 
out any  elevation  of  temperature,  in  spite  of  the  attraction  of 
Cohesion. 

Mrs.  B.  It  is  because  the  degree  of  heat  at  which  we  usually 
observe  these  fluids  is  sufficient  to  overcome  'their  attraction  of 
cohesion.  Ether  is  of  this  description  ;  it  will  boil  and  be  con- 
verted into  vapour,  at  the  common  temperature  of  the  air,  if 
the  pressure  of  the  atmosphere  be  taken  oft'. 

Emily  1  thought  that  ether  would  evaporate  without  either 
the  pressure  of  the  atmosphere  being  taken  a  way,  or  heat  appli- 
ed ;  and  that  it  was  for  that  reason  so  necessary  to  keep  it  care- 
fully corked  up? 

JV,rs.  -''.  It  is  true  it  will  evaporate,  but  without  ebullition ; 
what  1  am  now  speaking  of  is  the  vaporization  of  ether,  or  its 
conversion  into  vapour  by  tailing.  1  am  going  to  shoiv  you 
how  suddenly  the  ether  in  this  phial  will  be  converted  into  va- 
pour, by  means  of  the  air-pump. — Observe  with  what  rapidity 
the  bubbles  ascend,  as  I  take  off  the  pressured  the  atmosphere. 

Caroline.  It  positively  boils  :  how  singular  10  see  a  liquid 
boil  without  rieat! 

Mrs.  B.  Now  I  shall  place  the  phial  of  ether  in  this  glass, 
which  it  nearly  fits,  so  as  to  leave  only  a  small  sp;ice,  which  I 
fill  with  water;  and  in  this  state  I  put  it  again  under  the  receiv- 
er. (PLATE  IV.  Fig.  1.)* — You  will  observe,  as  1  exhaust  the 
air  from  it,  that  whilst  the  ether  boils,  the  water  freezes. 

*  Two  pieces  of  thin  ,e;U<s.s  tubes,  Si  aled  alone  end  nrsuit.  answer  this 
purpose  better.  The  experiment,  however,  as  here  fit-sen' bed,  Is  diffi- 
cult, and  requires  a  very  nice  apparatus.  But  ir,  instead  oi  im;a!s  or 
tubes,  two  watch  glasses  be  used,  wator  may  i>r  frciZ  -n  almosi  instant- 
ly in  the  same  manner.  The  two  Classes  are  placed  over  one  another, 
w  th  a  few  drops  of  water  interposed  between  thc-in.  r  n4  the  uppermost 
glass  is  (illed  with  ether.  After  working  the  pump  \>  r  a  mumtt;  or 
two,  the  glasses  are  found  to  adhere  strongly  together,  and  a  thin  lay- 
«?r  of  ice  is  seen  between  them. 

6* 


54  #BEE   CALORIC. 

Caroline.  It  is  indeed  wonderful  to  see  water  freeze  in  con- 
tact with  a  boiling  fluid  ! 

Emily.  I  am  at  a  loss  to  conceive  how  the  ether  can  pass  to 
the  state  of  vapour  without  an  addition  of  caloric.  Does  it  not 
contain  more  caloric  in  a  state  of  vapour,  than  in  a  state  of  li- 
quidity ? 

Mrs.  B.  It  certainly  does ;  for  though  it  is  the  pressure  of 
the  atmosphere  which  condenses  it  into  a  liquid,  it  is  by  forcing 
out  the  caloric  that  belongs  to  it  when  in  an  aeViform  state. 

Emily.  You  have,  therefore,  two  difficulties  to  explain,  Mrs. 
B. — First,  whence  the  ether  obtains  the  caloric  necessary  to 
convert  it  into  vapour  when  it  is  relieved  from  the  pressure  of 
the  atmosphere;  and,  secondly,  what  is  the  reason  that  the  wa- 
ter, in  which  the  bottle  of  ether  stands,  is  frozen  ? 

Caroline.  Now,  I  think,  1  can  answer  both  these  questions. 
The  ether  obtains  the  addition  of  caloric  required,  from  the 
•water  in  the  glass;  and  the  loss  of  caloric,  which  the  latter  sus- 
tains, is  the  occasion  of  its  freezing. 

Mrs.  B.  You  are  perfectly  right ;  and  if  you  look  at  the 
thermometer  which  1  have  placed  in  the  water,  whilst  I  am 
working  the  pump,  you  will  see  that  every  time  bubbles  of  va- 
pour are  produced,  the  mercury  descends;  which  proves  that 
the  heat  of  the  water  diminishes  in  proportion  as  the  ether 
boils. 

Emily.  This  I  understand  now  very  well ;  but  if  the  water 
freezes  in  consequence  of  yielding  its  caloric  to  the  ether,  the 
equilibrium  of  heat  must,  in  this  case,  be  totally  destroyed. 
Yet  you  have  told  us,  that  the  exchange  of  caloric  between  two 
bodies  of  equal  temperature,  was  always  equal;  how,  then,  is 
it  that  the  water,  which  was  originally  of  the  same  temperature 
as  the  ether,  gives  out  caloric  to  it,  till  the  water  is  frozen,  and 
the  ether  made  to  boil  ? 

Mrs.  B.  I  suspected  that  you  would  make  these  objections  ; 
and,  in  order  to  remove  them,  I  enclosed  two  thermometers  in 
the  air-pump  ;  one  of  which  stands  hi  the  glass  of  water,  the 
other  in  the  phial  of  ether;  and  you  may  see  that  the  equilib- 
rium of  temperature  is  not  destroyed;  for  as  the  thermometer 
descends  in  the  water,  that  in  the  ether  sinks  in  the  same  man- 
ner; so  that  both  thermometers  indicate  the  same  temperature, 
though  one  of  them  is  in  a  boiling,  the  other  in  a  freezing  li- 
quid. 

Emily.  The  ether,  then,  becomes  colder  as  it  boils  ?  This  is 
So  contrary  to  common  experience,  that  I  confess  it  astonishes 
me  exceedingly. 


FREE  CALORIC,  55 

Caroline.  It  is,  indeed,  a  most  extraordinary  circumstance* 
But  pray,  how  do  you  account  for  it  ? 

Mrs.  ti.  I  cannot  satisfy  your  curiosity  at  present;  for  be- 
fore we  can  attempt  to  explain  this  apparent  paradox,  it  is 
necessary  to  become  acquainted  with  the  subject  of  LATENT 
HEAT  ;  and  that,  I  think,  we  must  defer  till  our  next  interview. 

Caroline.  I  believe,  Mrs.  B.,  thai  you  are  glad  to  put  off  the 
explanation  ;  for  it  must  be  a  very  difficult  point  to  account  for. 

Mrs.  B.  I  hope,  however,  that  I  shall  do  it  to  your  complete 
satisfaction. 

Emily.  But  before  we  part,  give  me  leave  to  ask  you  one 
question.  Would  not  water,  as  well  as  ether,  boil  with  less 
heat,  if  deprived  of  the  pressure  of  the  atmosphere? 

Mrs.  8.  Undoubtedly.  You  must  always  recollect  that  there 
are  two  forces  to  overcome,  in  order  to  make  a  liquid  boil  or 
evaporate;  the  attraction  of  aggregation,  and  the  weight  of  the 
atmosphere.  On  the  summit  of  a  high  mountain  (as  Mr.  I>e 
Saussure  ascertained  on  Mount  Blanc)  much  less  heat  is  requi- 
red to  make  water  boil,  than  in  the  plain,  where  the  weight  of 
the  atmosphere  is  greater.*  Indeed  if  the  weight  of  the  atmos- 
phere be  entirely  removed  by  means  of  a  good  air-pump,  and 
if  water  be  placed  in  the  exhausted  receiver,  it  will  evaporate 
so  fast,  however  cold  it  may  be,  as  to  give  it  the  appearance  of 
boiling  from  the  surface.  But  without  the  assistance  of  the 
air  pump,  I  can  show  you  a  very  pretty  experiment,  which 
proves  the  effect  of  the  pressure  of  the  atmosphere  in  this  re- 
spect. 

Observe,  that  this  Florence  flask  is  about  half  full  of  water,  and 
the  upper  half  of  invisible  vapour,  the  water  being  in  the  act  of 
boiling. — I  take  it  from  the  lamp,  and  cork  it  carefully— the 
water,  you  see,  immediately  ceases  boiling. — I  shall  now  dip 
the  flask  into  a  bason  of  cold  water. t 

Caroline.  But  look,  Mrs.  B.,  the  hot  water  begins  to  boil 
again,  although  the  cold  water  must  rob  it  more  and  more  of 
its  caloric  r  What  can  be  the  reason  of  that  ? 

Mrs.  B.  Let  us  examine  its  temperature.  You  see  the  ther- 
mometer immersed  in  it  remains  stationary  at  150  degrees, 
which  is  about  30  degrees  below  the  boiling  point.  When  I 
took  the  flask  from  the  lamp,  I  observed  to  you  that  the  upper 

*  On  the  top  of  Mount  Blanc,  water  boiled  when  heated  only  to 
187  degrees,  instead  of  212  degrees. 

t  f.'he  same  effect  may  be  produced  by  wrapping  a  cold  wet  linen 
cloth  round  the  upper  part  of  the  flask.  In  order  to.  show  how  much 
the  water  cools  whilst  it  is  boiling,  a  thermometer,  graduated  on  the 
tube  itself,  may  be  introduced  into  the  bottle  through  the  cork* 


56  FREE    CALORIC. 

part  of  it  was  filled  with  vapour  ;  this  being  compelled  to  yield 
its  caloric  to  the  cold  water,  was  again  condensed  into  water. — > 
What,  then,  filled  the  upper  part  of  the  flask? 

Emily.  Nothing;  for  it  was  too  well  corked  for  the  air  to 
gain  admittance,  and  therefore  the  upper  part  of  the  flask  must 
be  a  vacuum. 

Mrs.  h.  The  water  below,  therefore,  no  longer  sustains  the 
pressure  of  the  atmosphere,  and  will  consequently  boil  at  a  much 
lower  temperature.  Thus,  you  see,  though  it  had  lost  many  de- 
grees of  heat,  it  began  boiling  again  the  instant  the  vacuum  was 
formed  above  it.  The  boiling  has  now  ceased,  the  tempera- 
ture of  the  water  being  still  farther  reduced  ;  if  it  had  been 
ether,  instead  of  water,  it  would  have  continued  boiling  much 
longer,  for  ether  boils,  under  the  usual  atmospheric  pressure,  at 
a  temperature  as  low  as  100  degrees;  and  in  a  vacuum  it  boils 
at  almost  any  temperature;  but  water  being  a  more  dense  fluid, 
requires  a  more  considerable  quantity  of  caloric  to  make  it  evap- 
orate quickly,  even  when  the  pressure  of  the  atmosphere  is  re- 
moved. 

Emily.  What  proportion  of  vapour  can  the  atmosphere  con- 
tain in  a  state  of  solution  ? 

Mrs.  B.  I  do  not  know  whether  it  has  been  exactly  ascer- 
tained by  experiment ;  but  at  any  rate  this  proportion  must  va- 
ry, both  according  to  the  temperature  and  the  weight  of  the  at- 
mosphere ;  for  the  lower  the  temperature,  and  the  greater  the 
pressure,  the  smaller  must  be  the  proportion  of  vapour  that  the 
atmosphere  can  contain. 

To  conclude  the  subject  of  free  caloric,  I  should  mention 
Ignition,  by  which  s  meant  that  emission  of  light  which  is  pro- 
duced in  bodies  at  a  very  high  temperature,  and  which  is  the 
sffect  of  accumulated  caloric. 

Emily.  You  mean,  I  suppose,  that  light  which  is  produced 
by  a  burning  body  ? 

Mrs.  B.  No:  ignition  is  quite  independent  of  combustion. 
Clay,  chalk,  and  indeed  all  incombustible  substances,  may  be 
made  red  hot.  When  a  body  burns,  the  light  emitted  is  the 
effect  of  a  chemical  change  which  takes  place,  whilst  ignition 
is  the  effect  of  caloric  alone,  and  no  other  change  than  that  of 
temperature  is  produced  in  the  ignited  body. 

All  solid  bodies,  and  most  liquids,  are  susceptible  of  ignition, 
6r,  in  other  words,  of  being:  heated  so  as  to  become  luminous  ; 
and  it  is  remarkable  that  this  takes  place  pretty  nearly  at  the 
same  temperature  in  all  bodies,  that  is,  at  about  800  degrees  of 
Fahrenheit's  scale, 


•OMB1NED    CALORIC.  •(){ 

Emily.  But  how  can  liquids  attain  so  high  a  temperature, 
without  being  converted  into  vapour  ? 

Mrs  B.  By  means  of  confinement  and  pressure.  Water 
confined  in  a  strong  iron  vessel  (called  Papin's  digester)  can 
have  its  temperature  raised  to  upwards  of  400  degrees.  Sir 
James  Hall  has  made  some  very  curious  experiments  on  the  ef- 
fects of  heat  assisted  hy  pressure;  by  means  of  strong  gun- 
barrels,  he  succeeded  in  melting  a  variety  of  substances  which 
were  considered  as  infusible;  arid  it  is  not  unlikely  that,  by 
similar  methods,  water  itself  might  be  heated  to  redness. 

Emily.  I  am  surprised  at  that :  for  I  thought  that  the  force 
of  steam  was  such  as  to  destroy  almost  all  mechanical  resist- 
ance. 

Mrs.  B.  The  expansive  force  of  steam  is  prodigious  ;  but  in 
order  to  subject  water  to  such  high  temperatures,  it  is  prevent- 
ed by  confinement  from  being  converted  into  steam,  and  the 
expansion  of  heated  water  is  comparatively  trifling. — But  we 
have  dwelt  so  long  on  the  subject  of  free  caloric,  that  we  must 
reserve  the  other  modifications  of  that  agent  to  our  next  meet* 
ing,  when  we  shall  endeavour  to  proceed  more  rapidly. 


6ONVERSATION  IV. 

ON    COMBINED    CALORIC,    COMPREHENDING    SPECIFIC 
AND  LATENT  HEAT. 

Mrs.  B.  WE  are  now  to  examine  the  other  modifications  of 
Galoric. 

Caroline.  I  am  very  curious  to  know  of  what  nature  they  can 
be  ;  for  I  have  no  notion  of  any  kind  of  heat  that  is  not  per- 
ceptible to  the  senses. 

Mrs.  B.  In  order  to  enable  you  to  understand  them,  it  will 
be  necessary  to  enter  into  some  previous  explanations. 

It  has  been  discovered  by  modern  chemists,  that  bodies  of  a 
different  nature,  heated  to  the  same  temperature,  do  not  con- 
tain the  same  quantity  of  caloric. 

Caroline.  How  could  that  be  ascertained  ?  Have  you  not 
told  us  that  it  is  impossible  to  discover  the  absolute  quantity  of 
caloric  which  bodies  contain  ? 

Mrs.  B.  True ;  but  at  the  same  time  I  said  that  we  were 
enabled  to  form  a  judgment  of  the  proportions  which  bodies 
bore  to  each  other  in  this  respect.  Thus  it  is  found  that,  in 
order  to  raise  the  temperature  of  different  bodies  the  sanre 


•)S  COMBINED    CALORIC. 

number  of  degrees,  different  quantities  of  caloric  are  required 
for  each  of  them.  If,  for  instance,  you  plac^  a  pound  of  lead, 
a  pound  of  chalk,  and  a  pound  of  milk,  in  a  hot  oven,  they  will 
be  gradually  heated  to  the  temperature  of  the  oven  5  but  the 
lead  will  attain  it  first,  the  chalk  next,  and  the  milk  last. 

Caroline.  That  is  a  natural  consequence  of  their  different 
bulks ;  the  lead,  beingthe  smallest  body,  will  be  heated  soonest, 
and  the  milk,  which  is  the  largest,  will  require  the  longest 
time. 

Mrs.  B.  That  explanation  will  not  do,  for  if  the  lead  be  the 
least  in  bulk,  it  offers  also  the  least  surface  to  the  caloric,  the 
quantity  of  heat  therefore  which  can  enter  into  it  in  the  same 
space  of  time  is  proportionally  smaller. 

Emily.  Why,  then,  do  not  the  three  bodies  attain  the  tem- 
perature of  the  oven  at  the  same  time  ? 

Mrs.  B.  It  is  supposed  to  be  on  account  of  the  different 
capacity  of  these  bodies  for  caloric. 

Caroline.  What  do  you  mean  by  the  capacity  of  a  body  for 
caloric  ? 

Mrs.  B.  I  mean  a  certain  disposition  of  bodies  to  require 
more  or  less  caloric  for  raising  their  temperature  to  any  degree 
of  heat.  Perhaps  the  fact  may  be  thus  explained  : 

Let  us  put  as  many  marbles  into  this  glass  as  it  will  contain, 
and  pour  some  sand  over  them — observe  how  the  sand  pene- 
trates and  lodges  between  them.  We  shall  now  fill  another 
glass  with  pebbles  of  various  forms — you  see  that  they  arrange 
themselves  in  a  more  compact  manner  than  the  marbles,  which, 
being  globular,  can  touch  each  other  by  a  single  point  only. 
The  pebbles  therefore,  will  not  admit  so  much  sand  between 
them  ;  and  consequently  one .  of  these  glasses  will  necessarily 
contain  more  sand  than  the  other,  though  both  of  them  be 
equally  full. 

Caroline.  This  I  understand  perfectly.  The  marbles  and 
the  pebbles  represent  two  bodies  of  different  kinds,  and  the 
sand  the  caloric  contained  in  them;  and  it  appears  very  plain, 
from  this  comparison,  that  one  body  may  admit  of  more  caloric 
between  its  particles  than  another. 

Mrs.  B.  You  can  no  longer  be  surprised,  therefore,  that  bod- 
ies of  a  different  capacity,  for  caloric  should  require  different 
proportions  of  that  fluid  to  raise  their  temperatures  equally. 

Emily.  But  I  do  not  conceive  why  the  body  that  contains 
the  most  caloric  should  not  be  of  the  highest  temperature ; 
that  is  to  say,  feel  hot  in  proportion  to  the  quantity  of  caloric 
it  contains. 

Mrs.  B.  The  caloric  that  is  employed  in  filling  the  capacity 


COMBINED  CALORIC,  5$ 

of  a  body,  is  not  free  caloric  ;  but  is  imprisoned  as  it  were  in 
the  body,  and  is  therefore  imperceptible  :  for  we  can  feel  only 
the  caloric  which  the  body  parts  with,  and  not  that  which  it  re- 
tains. 

Caroline.  It  appears  to  me  very  extraordinary  that  heat 
should  be  confined  in  a  body  in  such  a  manner  as  to  be  imper- 
ceptible. 

Mrs.  B.  If  you  lay  your  hand  on  a  hot  body,  you  feel  only 
the  caloric  which  leaves  it,  and  enters  your  hand  ;  for  it  is  im- 
possible that  you  should  be  sensible  of  that  which  remains  in 
the  body.  The  thermometer,  in  the  same  manner,  is  affected 
only  by  the  free  caloric  which  a  body  transmits  to  it,  and  not 
at  all  by  that  which  it  does  not  part  with. 

Caroline.  I  begin  to  understand  it :  but  I  confess  that  the 
idea  of  insensible  heat  is  so  new  and  strange  to  me,  that  it  re- 
quires some  time  to  render  it  familiar. 

Mrs.  B.  Call  it  insensible  caloric,  and  the  difficulty  will  ap- 
pear much  less  formidable.  It  is  indeed  a  sort  of  contradic- 
tion to  call  it  heat,  when  it  is  so  situated  as  to  be  incapable  of 
producing  that  sensation.  Yet  this  modification  of  caloric  is 
commonly  called  SPECIFIC  HEAT. 

Caroline.  But  it  certainly  would  have  been  more  correct  to 
have  called  it  specifiic  caloric. 

Emily.  I  do  not  understand  how  the  term  specific  applies  to 
this  modification  of  caloric  ? 

Mrs.  B.  It  expresses  the  relative  quantity  of  caloric  which 
different  species  of  bodies  of  the  same  weight  and  temperature 
are  capable  of  containing.  This  modification  is  also  frequently 
called  heat  of  capacity,  a  term  perhaps  preferable,  as  it  ex- 
plains better  its  own  meaning. 

You  now  understand,  I  suppose,  why  the  milk  and  chalk  re- 
quired a  longer  portion  of  time  than  the  lead  to  raise  their  tem- 
perature to  that  of  the  oven  ? 

Emily.  Yes  :  the  milk  and  chalk  having  a  greater  capacity 
for  caloric  than  the  lead,  a  greater  proportion  of  that  fluid  be- 
came insensible  in  those  bodies  :  and  the  more  slowly,  thereforef 
their  temperature  was  raised. 

Caroline.  But  might  not  this  difference  proceed  from  the  dif- 
ferent conducting  powers  of  heat  in  these  three  bodies,  since 
that  which  is  the  best  conductor  must  necessarily  attain  the 
temperature  of  the  oven  first  ? 

Mrs.  B  Very  well  observed,  Caroline.  This  objection 
would  be  insurmountable,  if  we  could  not,  by  reversing  the  ex- 
periment, prove  that  the  milk,  the  chalk,  and  the  lead,  actually 
absorbed  different  quantities  of  caloric,  and  we  know  that  if  the 


60  COMBINED    CALORIC. 

different  time  they  took  in  heating,  proceeded  merely  from  their 
different  conducting  powers,  they  would  each  have  acquired  an 
equal  quantity  of  caloric. 

Caroline.  Certainly.  But  how  can  you  reverse  this  experi- 
ment ? 

Mrs.  B.  It  may  be  done  by  cooling  the  several  bodies  to  the 
same  degree  in  an  apparatus  adapted  to  receive  and  measure 
the  caloric  which  they  give  out.  Thus,  if  you  plunge  them  in- 
to three  equal  quantities  of  water,  each  at  the  same  temperature, 
you  will  be  able  to  judge  of  the  relative  quantity  of  caloric  which 
the  three  bodies  contained,  by  that,  which,  in  cooling,  they  com- 
municated to  their  respective  portions  of  water :  for  the  same 
quantity  of  caloric  which  they  each  absorbed  to  raise  their  tem- 
perature, will  abandon  them  in  lowering  it ;  and  on  examining 
the  three  vessels  of  water,  you  will  find  the  one  in  which  you 
immersed  the  lead  to  be  the  least  heated ;  that  which  held  the 
chalk  will  be  the  next ;  and  that  which  contained  the  milk  will 
be  heated  the  most  of  all.  The  celebrated  Lavoisier  has  inven- 
ted a  machine  to  estimate,  upon  this  principle,  the  specific  heat 
of  bodies  in  a  more  perfect  manner ;  but  1  cannot  explain  it  to 
you,  till  you  are  acquainted  with  the  next  modification  of  ca- 
loric. 

Emily.  The  more  dense  a  body  is,  I  suppose,  the  less  is  its 
capacity  for  caloric  ? 

Mrs.  B.  This  is  not  always  the  case  with  bodies  of  different 
nature  ;  iron,  for  instance,  contains  more  specific  heat  than  tin, 
though  it  is  more  dense.  This  seems  to  show  that  specific  heat 
does  not  merely  depend  upon  the  interstices  between  the  parti- 
cles ;  but,  probably,  also  upon  some  peculiar  constitution  of 
the  bodies  which  we  do  not  comprehend. 

Emily.  But,  Mrs.  B.,  it  would  appear  to  me  more  proper  to 
compare  bodies  by  measure,  rather  than  by  weight,  in  order  to 
estimate  their  specific  heat.  Why,  for  instance,  should  we 
not  compare  pints  of  milk,  of  chalk,  and  of  lead,  rather  than 
pounds  of  those  substances  :  for  equal  weights  may  be  compo- 
sed of  very  different  quantities  ? 

Mrs.  B.  You  are  mistaken,  my  dear  ;  equal  weight  must 
contain  equal  quantities  of  matter  ;  and  when  we  wish  to  know 
what  is  th^  relative  quantity  of  caloric  which  substances  of  va- 
rious kinds  are  capable  of  containing  under  the  same  tempera- 
turn,  we  must  compare  equal  weights,  and  not  equal  bulks  of 
those  substances.  Bodies  of  the  same  weight  may  undoubtedly 
be  of  very  different  dimensions  ;  but  that  docs  not  change 
their  real  quantity  of  matter.  A  pound  of  feathers  does  n at 
Contain  one  atom  more  than  a  pound  of  lead. 


COMBINED    CALORIC.  (jt. 

Caroline..  I  have  another  difficulty  to  propose.  It  appears 
to  me,  that  if  the  temperature  of  the  three  bodies  in  the  oven, 
did  not  rise  equally,  they  would  never  reach  the  same  degree  ; 
the  lead  would  always  keep  its  advantage  over  the  chalk  and 
milk,  and  would  perhaps  be  boiling  before  the  others  had  at- 
tained the  temperature  of  the  oven.  I  think  you  might  as  well 
say  that,  in  the  course  of  time,  you  and  I  should  be  of  the  same 
age  ? 

Mrs.  B.  Your  comparison  is  not  correct,  Caroline.  As  soon 
as  the  lead  reached  the  temperature  of  the  oven,  it  would  re- 
main stationary  ;  for  it  would  then  give  out  as  much  heat  as  it 
would  receive.  You  should  recollect  that  the  exchange  of  ra- 
diating heat,  between  two  bodies  of  equal  temperature,  is  equal : 
it  would  be  impossible,  therefore,  for  the  lead  to  accumulate 
heat  after  having  attained  the  temperature  of  the  oven  ;  and 
that  of  the  chalk  and  milk  therefore  would  ultimately  arrive  at 
the  same  standard.  Now  I  fear  that  this  will  not  hold  good 
with  respect  to  our  ages,  and  that,  as  long  as  I  live,  I  shall  nev- 
er cease  to  keep  my  advantage  over  you. 

Emily.  I  think  that  I  have  found  a  comparison  'for  specific 
heat,  which  is  very  applicable.  Suppose  that  two  men  of  equal 
weight  and  bulk,  but  who  required  different  quantities  of  food 
to  satisfy  their  appetites,  sit  down  to  dinner,  both  equally  hun- 
gry; the  one  would  consume  a  much  greater  quantity  of  provi- 
sions than  the  other,  in  order  to  be  equally  satisfied. 

Mrs.  B.  Yes,  that  is  very  fair;  for  the  quantity  of  food  ne- 
cessary to  satisfy  their  respective  appetites,  varies  in  the  sume 
manner  as  the  quantity  of  caloric  requisite  to  raise  equally  the 
temperature  of  different  bodies. 

Emily.  The  thermometer,  then,  affords  no  indication  of  the 
specific  heat  of  bodies  ? 

Mrs.  B.  None  at  all :  no  more  than  satiety  is  a  test  of  the 
quantity  of  food  eaten.  The  thermometer,  as  I  have  repeat- 
edly said,  can  be  affected  only  by  free  caloric,  which  alone  rai- 
ses the  temperature  of  bodies. 

But  there  is  another  mode  of  proving  the  existence  of  spe- 
cific heat,  which  affords  a  very  satisfactory  illustration  of  that 
modification.  This,  however,  I  did  not  enlarge  upon  before, 
as  I  thought  it  might  appear  to  you  rather  complicated. — If 
you  mix  two  fluids  of  different  temperatures,  let  us  say  the  one  at 
50  degrees,  and  the  other  at  100  degrees,  of  what  temperature 
do  you  suppose  the  mixture  will  be  ? 

Caroline.  It  will  be  no  doubt  the  medium  between  the  twos 
that  is  to  say,  75  degrees. 

Mrs,  B.  'That  will  be  the  case  if  the  two  bodies  happen  tc 

r 


OH  COMBINED    CALORIC. 

have  the  same  capacity  for  caloric;  but  if  not,  a  different  re- 
sult will  be  obtained.  Thus,  for  instance,  if  you  mix  togeth- 
er a  pound  of  mercury,  heated  at  50  degrees,  and  a  pound  of 
water  heated  at  100  degrees,  the  temperature  of  the  mixture, 
instead  of  being  75  degrees,  will  be  80  degrees  ;  so  that  the  wa- 
ter will  have  lost  only  12  degrees,  whilst  the  mercury  will  have 
gained  38  degrees  ;  from  which  you  will  conclude  that  the  ca- 
pacity of  mercury  for  heat  is  less  than  that  of  water. 

Caroline.  I  wonder  that  mercury  should  have  so  little  spe- 
cific heat.  Did  we  not  see  it  was  a  much  better  conductor  of 
heat  than  water  ? 

Mrs.  B.  And  it  is  precisely  on  that  account  that  its  specific 
heat  is  less.  For  since  the  conductive  power  of  bodies  de- 
pends, as  we  have  observed  before,  on  their  readiness  to  receive 
heat  and  part  with  it,  it  is  natural  to  expect  that  those  bodies 
which  are  the  worst  conductors  should  absorb  the  most  caloric 
before  they  are  disposed  to  part  with  it  to  other  bodies.  But 
let  us  now  proceed  to  LATENT  HEAT. 

Caroline.  And  pray  what  kind  of  heat  is  that  ? 

Mrs.  Jl.  It  is  another  modification  of  combined  caloric, 
which  is  so  analogous  t»  specific  heat,  that  most  chemists  make 
no  distinction  between  them  ;  but  Mr.  Pictet,  in  his  Essay  on 
Fire,  has  so  clearly  discriminated  them,  that  I  am  induced  to 
adopt  his  view  of  the  suhject.  We  therefore  call  latent  heat 
that  portion  of  insensible  caloric  which  is  employed  in  changing 
the  state  of  bodies;  that  is  to  say,  in  converting  solids  into  li- 
quids, or  liquids  into  vapour.  When  a  body  changes  its  state 
from  solid  to  liquid,  or  from  liquid  to  vapour,  its  expansion  oc- 
casions a  sudden  and  considerable  increase  of  capacity  for  heat, 
in  consequence  of  which  it  immediately  absorbs  a  quantity  of 
caloric,  which  becomes  fixed  in  the  body  it  has  transformed; 
and,  as  it  is  perfectly  concealed  from  our  senses,  it  has  obtained 
the  name  of  latent  heat. 

Caroline.  I  think  it  would  be  much  more  correct  to  call  this 
modification  latent  caloric  instead  of  latent  heat,  since  it  does 
not  excite  the  sensation  of  heat. 

Mrs.  B.  This  modification  of  heat  was  discovered  and  na- 
med by  Dr.  Black  long  before  the  French  chemists  introduced 
lhe  term  caloric,  and  we  must  not  presume  to  alter  it,  as  it  is 
still  used  by  much  better  chemists  than  ourselves.  Besides, 
you  are  not  to  suppose  that  the  nature  of  heat  is  altered  by  be- 
ing variously  modified  :  for  if  latent  heat  and  specific  heat  do 
not  excite  the  same  sensations  as  free  caloric,  it  is  owing  to  their 
being  in  a  state  of  confinement,  which  prevents  them  from  ac- 
ting upon  our  organs  5  and  consequently,  as  soon  as  they  are 


COMBINED    CALORIC. 

^xtricated  from  the  body  in  which  they  are  imprisoned,  they  re- 
turn to  their  state  of  free  caloric. 

Emily.  But  I  do  not  yet  clearly  see  in  what  respect  latent 
;ieat  differs  from  specific  heat ;  for  they  are  both  of  them  im- 
prisoned and  concealed  in  bodies. 

Mrs.  B.  Specific  heat  is  that  which  is  employed  in  filling  the 
<  ap-icity  of  a  body  for  caloric,  in  the  stale  in  which  this  body  ac- 
lually  exists;  while  latent  heat  is  that  which  is  employed  only 
in  effecting  u  change  of  state,  that  is,  in  converting  bodies  from 
a  solid  to  a  liquid,  or  from  a  liquid  to  an  aeriform  state.  But  I 
think  that,  in  a  general  point  of  view,  both  these  modifications 
might  be  comprehended  under  the  name  of  heat  of  capacity,  as 
in  both  cases  the  caloric  is  equally  engaged  in  filling  the  capaci- 
ties of  bodies. 

I  shall  now  show  you  an  experiment,  which  I  hope  will  give 
you  a  clear  idea  of  what  is  understood  by  latent  heat. 

The  snow  which  you  see  in  this  phial  has  been  cooled  by 
certain  chemical  means  (which  I  cannot  well  explain  to  you  at 
present,)  to  five  or  six  degrees  below  the  freezing  point,  as  you 
will  find  indicated  by  the  thermometer  which  is  placed  in  it. 
We  shall  expose  it  to  the  heat  of  a  lamp,  and  you  will  see  the 
thermometer  gradually  rise,  till  it  reaches  the  freezing  point 

Emily,  But  there  it  stops,  Mrs.  B.,  and  yet  the  lamp  burns 
ust  as  well  as  before.  Why  is  not  its  heat  communicated  to 
the  thermometer  ? 

Caroline.  And  the  snow  begins  to  melt,  therefore  it  must  be 
rising  above  the  freezing  point  ? 

Mrs.  B.  The  heat  no  longer  affects  the  thermometer,  because 
it  is  wholly  employed  in  converting  the  ice  into  water.  As  the 
ice  melts,  the  caloric  becomes  latent  in  the  new-formed  liquid, 
;nd  therefore  cannot  raise  its  temperature;  and  the  thermome- 
ter will  consequently  remain  stationary,  till  the  whole  of  the  ice 
be  melted. 

Caroline.  Now  it  is  all  melted,  and  the  thermometer  begins 
to  rise  again. 

Mrs.  ft.  Because  the  conversion  of  the  ice  into  water  being 
completed,  the  caloric  no  longer  becomes  latent;  and  therefore 
••he  heat  which  the  water  now  receives  raises  its  temperature,  as 
you  find  the  thermometer  indicates. 

Emily.  LJi.it  I  do  not  think  that  the  thermometer  rises  so 
quickly  in  the  water  as  it  did  in  the  ice,  previous  to  its  begin- 
ning to  melt,  though  the  lamp  burns  equally  well  ? 

Mrs.  B.  That  is  owing  to  the  different  specific  heat  of  ice 
and  water.  The  capacity  of  water  for  caloric  being  greater 
than  that  of  ice,  more  heat  is  required  to  raise  its  temperature, 


$4  COMBINED    CALORIC. 

and  therefore  the  thermometer  rises  slower  in  the  water  than  in 
the  ice. 

Emily.  True  ;  you  said  that  a  solid  body  always  increased 
its  capacity  for  heat  by  becoming  fluid  ;  and  this  is  an  instance 
of  it. 

Mrs.  B.  Yes  ;  and  the  latent  heat  is  that  which  is  absorbed 
in  consequence  of  the  greater  capacity  which  the  water  has  for 
heat,  in  comparison  to  ice. 

I  must  now  tell  you  a  curious  calculation  founded  on  that 
consideration.  I  have  before  observed  to  you  that  though  the 
thermometer  shows  us  the  comparative  warmth  of  bodies,  and 
enables  us  to  determine  the  same  point  at  different  times  and 
places,  it  gives  us  no  idea  of  the  absolute  quantity  of  heat  in 
any  body.  We  cannot  tell  how  low  it  ought  to  fall  by  the  pri- 
vation of  all  heat,  but  an  attempt  has  been  made  to  infer  it  in 
the  following  manner.  It  has  been  found  by  experiment,  that 
(.he  capacity  of  water  for  heat,  when  compared  with  that  of 
ice,  is  as  10  to  9  5  so  that,  at  the  same  temperature,  ice  con- 
tains one-tenth  of  caloric  less  than  water.  By  experiment  also 
it  is  observed,  that  in  order  to  melt  ice,  there  must  be  added  to 
it  as  much  heat  as  would,  if  it  did  not  melt  it,  raise  its  temper- 
ature 140  degrees.*  This  quantity  of  heat  is  therefore  absorb- 
ed when  the  ice,  by  being  converted  into  water,  is  made  to 
contain  one-ninth  more  caloric  than  it  did  before.  Therefore 
140  degrees  is  a  ninth  part  of  the  heat  contained  in  ice  at  30 
degrees ;  and  the  point  of  zero,  or  the  absolute  privation  of 
heat,  must  consequently  be  1260  degrees  below  32  degrees.f 

This  mode  of  investigating  so  curious  a  question  is  ingenious, 
but  its  correctness  is  not  yet  established  by  similar  calculations 
for  other  bodies.  The  points  of  absolute  cold,  indicated  by 
this  method  in  various  bodies,  are  very  remote  from  each  other  ; 
it  is  however  possible,  that  this  may  arise  from  some  imperfec- 
tion in  the  experiments. 

Caroline.  It  is  indeed  very  ingenious — but  we  must  now  at- 
tend to  our  present  experiment.  The  water  begins  to  boih 
and  the  thermometer  is  again  stationary. 

*  That  is,  water  contains  140  degrees  of  heat  more  than  is  indica- 
ted by  the  thermometer.  C. 

t  This  calculation  was  made  by  Dr.  Irvine.  Dr.  Crawford  after- 
wards placed  the  real  zero  at  1500  degrees  below  the  0  of  Fahrenheit. 
Still  later  Mr.  Dalton  has  turned  his  attention  to  the  same  subject. 
The  mean  of  his  experiments  places  the  real  zero  6000  decrees  below 
the  freezing  point.  All  this  goes  to  show  that  very  little  has  yet  been 
demonstrated  on  this  difficult  question.  C, 


COMPOUND  CALORIC.  65 

Mra.  £.  Well,  Caroline,  it  is  your  turn  to  explain  the  phe- 
nomenon. 

Caroline.  It  is  wonderfully  curious  !  The  caloric  is  now  bu- 
sy in  changing  the  water  into  steam,  in  which  it  hides  itself,  and 
becomes  insensible.  This  is  another  example  of  latent  heat,' 
producing  a  change  of  form.  At  first  it  converted  a  solid  bo- 
dy into  a  liquid,  and  now  it  turns  the  liquid  into  vapour  ! 

Mrs.  B.  You  see,  my  dear,  how  easily  you  have  become  ac- 
quainted with  these  modifications  of  insensible  heat,  which  at 
first  appeared  so  unintelligible.  If,  now,  we  were  to  reverse 
these  changes,  and  condense  the  vapour  into  water,  and  the  wa- 
ter into  ice.  the  kitent  heat  would  re-appear  entirely,  in  the  form 
of  free  caloric. 

Emily.  Pray  do  let  us  see  the  effect  of  latent  heat  returning 
to  its  free  state. 

Mrs.  B.  For  the  purpose  of  showing  this,  we  need  simply 
conduct  the  vapour  through  this  tube  into  this  vessel  of  cold  wa- 
ter, where  it  will  part  with  its  latent  heat  and  return  to  its  liquid 
form. 

Emily.  How  rapidly  the  steam  heats  the  water  ! 

Mrs.  B.  That  is  because  it  does  not  merely  impart  its  free 
caloric  to  the  water,  but  likewise  its  latent  he-it.  This  method 
of  heating  liquids,  has  been  turned  to  advantage,  in  several 
economical  establishments.  The  steam-kitchens,  which  are 
getting  into  such  general  use,  are  upon  the  same  principle.  The 
steam  is  conveyed  through  a  pipe  in  a  simitar  manner,  into  the 
several  vessels  which  contain  the  provisions  to  be  dressed,  where 
it  communicates  to  them  its  latent  caloric,  and  returns  to  the 
state  of  water.  Count  Rum  ford  makes  great  use  of  this  princi- 
ple in  many  of  his  fire-places  :  his  grand  rnaxira  is  to  avoid  all 
unnecessary  waste  of  caloric,  for  which  purpose  he  confines  the 
heat  in  such  a  manner,  that  not  a  particle  of  it  shall  unnecessa- 
rily escape;  and  while  he  economises  the  free  caloric,  he  takes 
tare  also  to  turn  the  latent  heat  to  advantage.  It  is  thus  that 
he  is  enabled  to  produce  a  degree  of  heat  superior  to  that  which 
is  obtained  in  common  fire-places,  though  he  employs  loss  fuel. 

Emily.  When  the  advantages  of  such  contrivances  are  so 
clear  and  plain,  I  cannot  understand  why  they  are  not  univer- 
sally used. 

Mrs.  B.  A  long  time  is  always  required  before  innovations, 
however  useful,  can  be  reconciled  with  the  prejudices  of  the 
vulgar. 

Emily.  What  a  pity  it  is  that  there  should  be  a  prejudice 
against  new  inventions  j  how  much  more  rapidly  the  world 

7* 


COMBINED 

would  improve,  if  such  useful  discoveries  were  immediately  and 
universally  adopted  ! 

Mrs.  B.  1  believe,  my  dear,  that  there  are  as  many  novelties 
attempted  to  be  introduced,  the  adoption  of  which  would  be 
prejudicial  to  society,  as  there  are  of  those  which  would  be 
beneficial  to  it.  The  well-informed,  though  by  no  means  ex- 
empt from  error,  have  an  unquestionable  advantage  over  the 
illiterate,  in  judging  what  is  likely  or  not  to  prove  serviceable  ; 
and  therefore  we  find  the  former  more  ready  to  adopt  such  dis- 
coveries as  promise  to  be  really  advantageous,  than  the  latter, 
who  having  no  other  test  of  the  value  of  a  novelty  but  time  and 
experience,  at  first  oppose  its  introduction.  The  well-inform- 
ed, however,  are  frequently  disappointed  in  their  most  san- 
guine expectations,  and  the  prejudices  of  the  vulgar,  though 
they  often  retard  the  progress  of  knowledge,  yet  sometimes,  it 
must  be  admitted,  prevent  the  propagation  of  error. — But  we 
are  deviating  from  our  subject. 

We  have  converted  steam  into  water,  and  are  now  to  change 
water  into  ice,  in  order  to  render  the  latent  heat  sensible,  as  it 
escapes  from  the  water  on  its  becoming  solid.  For  this  purpose 
tye  must  produce  a  degree  of  cold  that  will  make  water  freeze. 

Caroline.  That  must  be  very  difficult  to  accomplish  in  this 
warm  room. 

Mrs.  B.  Not  so  much  as  you  think.  There  are  certain 
•liemical  mixtures  which  produce  a  rapid  change  from  the  solid 
Co  the  fluid  state,  or  the  reverse,  in  the  substances  combined,  in 
consequence  of  which  change  latent  heat  is  either  extricated  or 
absorbed. 

Emily.  I  do  not  quite  understand  you 

Mrs.  B.  This  snow  and  salt,  which  you  see  me  mix  togeth- 
er, are  melting  rapidly  ;  heat,  therefore,  must  be  absorbed  by 
the  mixture,  and  cold  produced. 

Caroline.  It  feels  even  colder  than  ice,  and  yet  the  snow  is 
melted.  This  is  very  extraordinary. 

Mrs.  B.  The  cause  of  the  intense  cold  of  the  mixture  is  to 
be  attributed  to  the  change  from  a  solid  to  a  fluid  state.  The 
nnion  of  the  snow  and  salt  produces  a  new  arrangement  of 
their  particles,  in  consequence  of  which  they  become  liquid  ; 
and  the  quantity  of  caloric,  required  to  effect  this  change,  is 
seized  upon  by  the  mixture  wherever  it  can  be  obtained.  This 
eagerness  of  the  mixture  for  caloric,  during  its  liquefaction,  is 
such,  that  it  converts  part  of  its  own  free  caloric  into  latent 
heat,  and  it  is  thus  that  its  temperature  is  lowered. 

Emily.  Whatever  you  put  in  this  mixtuse,  therefore,,  would 
freeze  ? 


COMBINED   CALORIC, 

Mr*.  B.  Yes  5  at  least  any  fluid  that  is  susceptible  of  freezing 
at  that  temperature.  I  have  prepared  this  mixture  of  salt  and 
snow  for  the  purpose  of  freezing  the  water  from  which  you  are 
desirous  of  seeing  the  latent  heat  escape.  I  have  put  a  ther- 
mometer in  the  glass  of  water  that  is  to  be  frozen,  in  order 
that  you  may  see  how  it  cools. 

Caroline.  The  thermometer  descends,  but  the  heat  which 
the  water  is  now  losing,  is  its  free,  not  its  latent  heat. 

Mrs.  ti.  Certainly  ;  it  does  not  part  with  its  latent  heat  till  it 
changes  its  state  and  is  converted  into  ice. 

Emily.  But  here  is  a  very  extraordinary  circumstance  !  The 
thermometer  has  fallen  below  the  freezing  point,  and  yet  the 
water  is  not  frozen.* 

Mrs.  />'.  That  is  always  the  case  previous  to  the  freezing  of 
water  when  it  is  in  a  state  of  rest.  Now  it  begins  to  congeal, 
and  you  may  observe  that  the  thermometer  again  rises  to  the 
freezing  point. 

Caroline.  It  appears  to  me  very  strange  that  the  thermome- 
ter should  rise  the  very  moment  that  the  water  freezes  ;  for  it 
seems  to  imply  that  the  water  was  colder  before  it  froze  than 
when  in  the  act  of  freezing. 

Mrs.  B.  It  is  so  :  and  after  our  long  dissertation  on  this  cir- 
cumstance, I  did  not  think  it  would  appear  so  surprising  to  you. 
Reflect  a  little,  and  I  think  you  will  discover  the  reason  of  it. 

Caroline.  It  must  be,  no  doubt,  the  extrications  of  latent 
heat,  at  the  instant  the  water  freezes,  which  raises  the  temper- 
ature. 

JWrs.  B.  Certainly ;  and  if  you  now  examine  the  thermome- 
ter, you  will  find  that  its  rise  was  but  temporary,  and  lasted  on- 
ly during  the  disengagement  of  the  latent  heat — now  that  all  the 
water  is  frozen  it  falls  again,  and  will  continue  to  fall  till  the  ice 
and  mixture  are  of  an  equal  temperature. 

Emily.  And  can  you  show  us  any  experiments  in  which  li- 
quids, by  being  mixed,  become  solid,  and  disengage  latent  heat  ? 

Mrs.  B.  I  could  show  you  several ;  bat  you  are  not  yet  suf- 
ficiently advanced  to  understand  them  well.  I  shall,  however, 
try  one,  which  will  afford  you  a  striking  instance  of  the  fact. 
The  fluid  which  you  see  in  this  phial  consists  of  a  quantity  of 
a  certain  salt  called  muriat  of  lime)  dissolved  in  water.  Now, 

*  To  make  this  experiment  striking,  the  glass  containing  the  water 
and  thermometer  ought  to  he  kept  perfectly  still  until  the  mercury 
sinks  below  the  freezing  point  Then  agitate  the  water,  or  drop  into 
it  a  small  piece  of  ice,  and  it  instantly  shoots  into  crystal3.  anHI  tfi< 
thermometer  rises.  €. 


68  COMBINED   CALORlfc. 

if  I  pour  into  it  a  few  drops  of  this  other  fluid,  called  sulphuric 
acid,  the  whole,  or  very  nearly  the  whole,  will  be  instantane- 
ously converted  into  a  solid  mass. 

Emily.  How  white  it  turns  !  I  feel  the  latent  heat  escaping, 
for  the  bottle  is  warm,  and  the  fluid  is  changed  to  a  solid  white 
substance  like  chalk  !* 

Caroline.  This  is,  indeed,  the  most  curious  experiment  we 
have  seen  yet.  But  pray  what  is  that  white  vapour,  which  as- 
cends from  the  mixture  ? 

Mrs.  B.  You  are  not  yet  enough  of  a  chemist  to  understand 
that. — But  take  care,  Caroline,  do  not  approach  too  near  it,  for 
it  has  a  very  pungent  smell. 

I  shall  show  you  another  instance  similar  to  that  of  the  wa- 
ter, which  you  observed  to  become  warmer  as  it  froze.  I  have 
in  this  phial  a  solution  of  a  salt  called  sulphat  of  soda  or  Glau- 
ber's salt,  made  very  strong,  and  corked  up  when  it  was  hot,  and 
kept  without  agitation  till  it  became  cold,  as  you  may  feel  the 
phial  is.  Now  when  I  take  out  the  cork  and  let  the  air  fall  upon 
it  (for  being  closed  when  boiling,  there  was  a  vacuum  in  the  up- 
per part)  observe  that  the  salt  will  suddenly  crystalize.  .  .  . 

Caroline.  Surprising !  how  beautifully  the  needles  of  salt 
have  shot  through  the  whole  phial ! 

Mrs.  B.  Yes,  it  is  very  striking — but  pray  do  not  forget  the 
object  of  the  experiment.  Feel  how  warm  the  phial  has  be- 
come by  the  conversion  of  part  of  the  liquid  into  a  solid. 

Emily*  Quite  warm  I  declare  !  this  is  a  most  curious  expe- 
riment of  the  disengagement  of  latent  heat. 

Mrs.  B.  The  slakeingof  lime  is  another  remarkable  instance 
of  the  extrication  of  latent  heat.  Have  you  never  observed 
how  quick-lime  smokes  when  water  is  poured  upon  it,  and  how 
much  heat  it  produces  ? 

Caroline.  Yes  ;  but  I  do  not  undeistand  what  change  of  state 
takes  place  in  the  lime  that  occasions  its  giving  out  latent  heat ; 
for  the  quick-lime,  which  is  solid,  is  (if  I  recollect  right)  re- 
duced to  powder,  by  this  operation,  and  is,  therefore,  rather 
Expanded  than  condensed. 

Mrs.  B.  It  is  from  the  water,  not  the  lime,  that  the  latent 
heat  is  set  free.  The  water  incorporates  with,  and  becomes 
solid  in  the  lime  ;  in  consequence  of  which  the  heat,  which 

*  The  sulphuric  acid  by  its  stronger  affinity  for  the  lime,  takes  it 
from  the  muriatic  acid,  unites  with  it,  and  forms  sulphate  of  lime.  The 
solidity  is  owing  to  the  insolubility  of  this  last  substance  in  water. 
The  experiment  succeeds  well  if  the  water  is, saturated  with  the  «in- 
riate.  C 


COMBINED   CALORIC.  69 

kept  it  in  a  liquid  state,  is  disengaged,  and  escapes  in  a  sensible 
form. 

Caroline.  I  always  thought  that  the  heat  originated  in  the 
lime.  It  seems  very  strange  that  water,  and  cold  water  too, 
should  contain  so  much  heat. 

Emily.  After  this  extrication  of  caloric,  the  water  must  exist 
in  a  state  of  ice  in  the  lime,  since  it  parts  with  the  heat  which 
kept  it  liquid. 

Mrs.  ':>.  It  cannot  properly  be  called  ice,  since  ice  implies  a 
degree  of  cold,  at  least  equal  to  the  freezing  point.  Yet  as  wa- 
ter, in  combining  with  lime,  gives  out  more  heat  than  in  free- 
zing, it  must  be  in  a  stale  of  still  greater  solidity  in  the  lime, 
than  it  is  in  the  forrn  of  ice  ;  and  you  may  have  observed  that 
it  does  not  moisten  or  liquefy  the  lime  in  the  smallest  degree. 

Emily.  But,  Mrs.  B.,  the  smoke  that  rises  is  white  ;  if  it 
was  only  pure  caloric  which  escaped,  we  might  feel,  but  could 
not  see  it. 

Mrs.  B.  This  white  vapour  is  formed  by  some  of  the  parti- 
cles of  lime,  in  a  state  of  fine  dust,  which  are  carried  off  by 
the  caloric. 

Emily.  In  all  changes  of  state,  then,  a  body  either  absorbs 
®r  disengages  latent  heat  ? 

Mrs.  B.  You  cannot  'exactly  say  absorbs  latent  heat,  as  the 
heat  becomes  latent  only  on  being  confined  in  the  body  ;  but. 
you  may  say,  generally,  that  bodies,  in  passing  from  a  solid  to 
a  liquid  form,  or  from  the  liquid  state  to  that  of  vapour,  absorb 
heat ;  and  that  when  the  reverse  takes  place,  heat  is  disenga- 
ged.* 

Emily.  We  can  now,  I  think,  account  for  the  ether  boiling, 
and  the  water  freezing  in  vacuo,  at  the  same  temperature.t 

Mrs.  B.  Let  me  hear  you  explain  it. 

Emily.  The  latent  heat,  which  the  water  gave  out  in  freezing, 
was  immediately  absorbed  by  the  ether,  during  its  conversion 
into  vapour  ;  and  therefore,  from  a  latent  state  in  one  liquid,  it 
passed  into  a  latent  state  in  the  other. 

Mrs.  B.  But  this  only  partly  accounts  for  the  result  of  the 
experiment ;  it  remains  to  be  explained  why  the  temperature 
of  the  ether,  while  in  a  state  of  ebullition,  is  brought  down  to 
the  freezing  temperature  of  the  water. — It  is  because  the  ether, 
during  its  evaporation,  reduces  its  own  temperature,  in  the 
same  proportion  as  that  of  the  water,  by  converting  its  free  ca- 

''"•  This  rule,  if  not  universal,  admits  of  very  few  exception., 


70  COMBINED    CALORIC. 

loric  into  latent  heat ;  so  that,  though  one  liquid  boils,  and  tht 
other  freezes,  their  temperatures  remain  in  a  state  of  equilibri- 
um. 

Emily.  But  why  does  not  welter,  as  well  as  ether,  reduce  its 
own  temperature  by  evaporating  ? 

Mrs.  B.  The  fact  is  that  it. does,  though  much  .'ess  rapidly 
than  ether.  Thus,  for  instance,  you  may  often  have  observed, 
in  the  heat  of  summer,  htfw  much  any  particular  spot  may  be 
cooled  by  watering,  though  the  water  used  for  that  purpose  be 
as  warm  as  the  air  itself.  Indeed  so  much  cold  may  be  produ- 
ced by  the  mere  evaporation  of  water,  that  the  inhabitants  of 
India,  by  availing  themselves  of  the  most  favourable  circum- 
stances for  this  process  which  their  warm  climate  can  afford, 
namely,  the  cool  of  the  night,  and  situations  most  exposed  to 
the  night  breeze,  succeed  in  causing  water  to  freeze,  though 
the  temperature  of  the  air  be  as  high  as  60  degrees.  The  wa- 
ter is  put  into  shallow  earthern  trays,  so  as  to  expose  an  exten- 
sive surface  to  the  process  of  evaporation,  and  in  the  morning, 
the  water  is  found  covered  with  a  thin  cake  of  ice,  which  is  col- 
lected in  sufficient  quantity  to  be  used  for  purposes  of  luxury. 

Caroline.  How  delicious  it  must  be  to  drink  liquids  so  cold 
in  those  tropical  climates  !  But,  Mrs.  B.,  could  we  not  try  that 
experiment  ? 

Mrs .  B.  If  we  were  in  the  country,  I  have  no  doubt  but 
that  we  should  be  able  to  freeze  water,  by  the  same  means,  and 
under  similar  circumstances.  But  we  can  do  it  immediately, 
upon  a  small  scale,  in  this  very  room,  in  which  the  thermome- 
ter stands  at  70  degrees.  For  this  purpose  we  need  only  place 
some  water  in  a  little  cup  under  the  receiver  of  the  air-pump 
PLATE. V.  fig.  1.,)  and  exhaust  the  air  from  it.  What  will  be 
the  consequence,  Caroline  ? 

Caroline.  Of  course  the  water  will  evaporate  more  quickU  . 
,-.ince  there  will  no  longer  be  any  atmospheric  pressure  on   it 
surface :  but  will  this  be  sufficient  to  make  the  water  freeze  ? 

Mrs.  B.  Probably  not,  because  the  vapour  will  not  be  car- 
ried off  fast  enough  j  but  this  will  be  accomplished  without  dii- 
ficulty  if  we  introduce  into  the  receiver  (fig.  1.,)  in  a  saucer,  01 
other  large  shallow  vessel,  some  strong  sulphuric  acid,  a  sub- 
stance which  has  a  great  attraction  for  water,  whether  in  the 
form  of  vapour,  or  in  the  liquid  state.  This  attraction  is  such 
that  the  acid  will  instantly  absorb  the  moisture  as  it  rises  from 
the  water,  so  as  to  make  room  for  the  formation  of  fresh  va- 
pour; this  \v-ll  of  course  hasten  the  process,  and  the  cold  pro- 
iiuce-i  from  the  rapid  evaporation  of  the  water,  will,  in  a  few 


1L4TE  77 


e  air  pump  &rtc*u>tr  /or  Mr.  Leth'es  experiment.  C<r  saucer  tJif/i    vnfp/iur/c 
aeid.  B  a  afafs  or  eartfttn  cu/>  cmrtamuy  toater*.  D  a  stand  /Gr  fa  ru*  uit/i  its 
k#s  mat/t  ^&us.  A  a  Thermometer.  Ft?.  2.  Dr.  JMaatM*  Cryvpfams.  Fy.  £.  Dr. 
farsstf  7,ux£  e/*Mi>i?dt  CryvjJu>n<t.Ftj.&&4;  t/is  aii/% rent  part?  o/ftj.S.  .rtenftfarate. 


6OMBINEU    CALORIC.  71 

minutes,  be  sufficient  to  freeze  its  surface.*  We  shall  now  ex- 
haust the  air  from  the  receiver. 

Emily.  Thousands  of  small  bubbles  already  rise  through 
the  water  from  the  internal  surface  of  the  cup ;  what  is  the  rea- 
son of  this  ? 

Mrs.  B.  These  are  bubbles  of  air  which  were  partly  attach- 
ed to  the  vessel,  and  partly  diffused  in  the  water  itself;  and 
they  expand  and  rise  in  consequence  of  the  atmospheric  pres- 
sure being  removed. 

Caroline.  See,  Mrs.  B. ;  the  thermometer  in  the  cup  is  sink- 
ing fast ;  it  has  already  descended  to  40  degrees  ! 

Emily.  The  water  seems  now  and  then  violently  agitated  on 
the  surface,  as  if  it  were  boiling  ;  and  yet  the  thermometer  is 
descending  fast ! 

Mrs.  B.  You  may  call  it  boiling  if  you  please,  for  this  ap- 
pearance is,  as  well  as  boiling,  owing  to  the  rapid  formation  of 
vapour $  but  here,  as  you  have  just  observed,  it  takes  place 
from  the  surface,  for  it  is  only  when  heat  is  applied  to  the  bot- 
tom of  the  vessel  that  the  vapour  is  formed  there. — Now  crys- 
tals of  ice  are  actually  shooting  all  over  the  surface  of  the  water* 

Caroline.  How  beautiful  it  is  !  The  surface  is  now  entirely 
frozen, — but  the  thermometer  remains  at  32  degrees. 

Mrs.  B.  And  so  it  will,  conformably  with  our  doctrine  of 
latent  heat,  until  the  whole  of  the  water  is  frozen  ^  but  it  will 
then  again  begin  to  descend  lower  and  lower,  in  consequence  of 
the  evaporation  which  goes  on  from  the  surface  of  the  ice. 

Emily.  This  is  a  most  interesting  experiment ;  but  it  would 
be  still  more  striking  if  no  sulphuric  acid  were  required. 

Mrs.  B.  I  will  show  you  a  freezing  instrument,  contrived  by 
Dr.  Woilaston,  upon  the  same  principle  as  Mr.  Leslie's  experi- 
ment, by  which  water  may  be  frozen  by  its  own  evaporation 
alone,  without  the  assistance  of  sulphuric  acid. 

This  tube,  which,  as  you  see  (PLATE  V.  fig.  2.,)  is  ter- 
minated at  each  extremity  by  a  bulb,  one  of  which  is  half  full 
of  water,  is  internally  perfectly  exhausted  of  air  ;  the  conse- 
quence of  this  is,  that  the  water  in  the  bulb  is  always  much  dis- 
posed to  evaporate.  This  evaporation,  however  does  not 
proceed  sufficiently  fast  to  freeze  the  water ;  but  if  the  empty 
ball  be  cooled  by  some  artificial  means,  so  as  to  condense  qiu>k- 
ly  the  vapour  which  rises  from  the  water,  the  process  may  be 
thus  so  much  promoted  as  to  cause  the  water  to  freeze  in  the 

*  This  experiment  was  first  devised  by  Mr.  Leslie,  and  has  since 
been  modified  in  a  variety  of  form*. 


72  COMBINED    CALORIC. 

other  ball.     Dr.  Wollaston  has  called  this  instrument  Crt/o- 
phoras.     \or  Frostbearer.  C.] 

Caroline.  So  that  cold  seems  to  perform  here  the  same  pail 
which  the  sulphuric  acid  acted  in  Mr.  Leslie's  experiment  ? 

Mrs.  B.  Exactly  so;  but  let  us  try  the  experiment. 

Etti.ily.  How  will  you  cool  the  instrument  ?  You  have  nei- 
ther ice  nor  snow. 

Mrs.  H.  True  ;  but  we  have  other  means  of  effecting  this.* 
You  recollect  what  an  intense  cold  can  be  produced  by  the  evap- 
oration of  ether  in  an  exhausted  receiver.  We  shall  inclose  the 
bulb  in  this  little  bag  of  fine  flannel  (fig.  3.),  then  soak  it  in 
ether,  and  introduce  it  into  the  receiver  of  the  air-pump,  fig.  5.) 
For  this  purpose  we  shall  find  it  more  convenient  to  use  a  cry- 
ophorus  of  this  shape  (fig.  4.),  as  its  elongated  bulb  passes  easi- 
ly through  a  brass  plate  which  closes  the  top  of  the  receiver, 
If  we  now  exhaust  the  receiver  quickly,  you  will  see,  in  less 
than  a  minute,  the  water  freeze  in  the  other  bulb,  out  of  the 
receiver. 

Emily.  The  bulb  already  looks  quite  dim,  and  small  drops 
of  water  are  condensing  on  its  surface. 

Caroline.  And  now  crystals  of  ice  shoot  all  over  the  water. 
This  is,  indeed,  a  very  curious  experiment! 

Mrs.  B.  You  will  see,  some  other  day,  that,  by  a  similar 
method,  even  quicksilver  may  be  frozen. — But  we  cannot  at 
present  indulge  in  any  further  digression. 

Having  advanced  so  far  on  the  subject  of  heat,  I  may  now 
give  you  an  account  of  the  calorimeter,  an  instrument  invented 
by  Lavoisier,  upon  the  principles  just  explained,  for  the  purpose 
of  estimating  the  specific  heat  of  bodies.  It  consists  of  a  vessel, 
the  inner  surface  of  which  is  lined  with  ice,  so  as  to  form  a  sort 
of  hollow  globe  of  ice,  in  the  midst  of  which  the  body,  whose 
specific  heat  is  to  be  ascertained,  is  placed.  The  ice  absorbs 
caloric  from  this  body,  till  it  has  brought  it  down  to  the  freez- 
ing point ;  this  caloric  converts  into  water  a  certain  portion  of 
the  ice  which  runs  out  through  an  aperture  at  the  bottom  of  the 
machine ;  and  the  quantity  of  ice  changed  to  water  is  a  test  of 
the  quantity  of  caloric  which  the  body  has  given  out  in  descend- 
ing from  a  certain  temperature  to  the  freezing  point. 

Caroline.  In  this  apparatus,  I  suppose,  the  milk,  chalk,  and 
lead,  would  melt  different  quantities  of  ice,  in  proportion  to  their 
different  capacities  for  caloric  ? 

*  This  mode  of  making  the  experiment  was  proposed,  and  the  par- 
ticulars detailed,  by  Dr.  Marcet.  in  the  "34th  vol.  of  Nicholson's  Jour- 
ntd,  p.  119.  . 


COMBINED    CALORlo.  7'3 

Mrs.  B.  Certainly:  and  thence  we  are  able  to  ascertain,  with 
precision,  their  respective  capacities  for  heat.  But  the  calo- 
rimeter affords  us  no  more  idea  of  the  absolute  quantity  of  heat 
contained  in  a  body,  than  the  thermometer;  for  though  by 
means  of  it  we  extricate  both  the  free  and  combined  caloric, 
yet  we  extricate  them  only  to  a  certain  degree,  which  is  the 
freezing  point ;  and  we  know  not  how  much  they  contain  of 
either  below  that  point. 

Emily.  According  to  the  theory  of  latent  heat,  it  appears  to 
me  that  the  weather  should  be  warm  when  it  freezes,  and  cold 
in  a  thaw  :  for  latent  heat  is  liberated  from  every  substance 
that  it  freezes,  and  such  a  large  supply  of  heat  must  warm  the 
atmosphere ;  whilst,  during  a  thaw,  that  very  quantity  of  free 
heat  must  be  taken  from  the  atmosphere,  and  return  to  a  latent 
state  in  the  bodies  which  it  thaws. 

Mrs.  B.  Your  observation  is  very  natural ;  but  consider  that 
in  a  frost  the  atmosphere  is  so  much  colder  than  the  earth,  that 
all  the  caloric  which  it  takes  from  the  freezing  bodies  is  insuffi- 
cient to  raise  its  temperature  above  the  freezing  point ;  other- 
wise the  frost  must  cease.  But  if  the  quantity  of  latent  heat  ex- 
tricated does  not  destroy  the  frost,  it  serves  to  moderate  the  sud- 
denness of  the  change  of  temperature  of  the  atmosphere,  at  the 
commencement  both  of  frost,  and  of  a  thaw.  In  the  first  in- 
stance, its  extrication  diminishes  the  severity  of  the  cold  ;  and, 
in  the  latter,  its  absorption  moderates  the  warmth  occasioned 
by  a  thaw  ;  it  even  sometimes  produces  a  discernable  chill,  at 
the  breaking  up  of  a  frost. 

Caroline.  But  what  are  the  general  causes  that  produce  those 
sudden  changes  in  the  weather,  especially  from  hot  to  cold, 
which  we  often  experience  ? 

Mrs.  B.  This  question  would  lead  us  into  meteorological 
discussions,  to  which  I  am  by  no  means  competent.  One  cir- 
cumstance, however,  we  can  easily  understand.  When  the  air 
has  passed  over  cold  countries,  it  will  probably  arrive  here  at  a 
temperature  much  below  our  own,  and  then  it  must  absorb 
heat  from  every  object  it  meets  with,  which  will  produce  a  gen- 
eral fall  of  temperature. 

Caroline.  But  pray,  now  that  we  know  so  much  of  the  effects 
of  heat,  will  you  inform  us  whether  it  is  really  a  distinct  body, 
or,  as  I  have  heard,  a  peculiar  kind  of  motion  produced  in  bod^ 
ies? 

Mrs.  B.  As  I  before  told  you,  there  is  yet  much  uncertain- 
ty as  to  the  nature  of  these  subtle  agents.  But  I  am  inclined 
to  consider  heat  not  as  a  mere  motion,  but  as  a  separate  sub- 
stance. Late  experiments  too  appear  to  make  it  a  compound 

5 


74  ELECTRO-CHEMISTRY. 

body,  consisting  of  the  two  electricities,  and  in  our  next  con- 
versation I  shall  inform  you  of  the  principal  facts  on  which  that 
opinion  is  founded. 


CONVERSATION  V. 

ON  THE  CHEMICAL  AGEN«  IE^  OF  ELECTRICITY.* 

Mrs.  B.  BEFORE  we  proceed  further  it  will  be  necessary  to 
give  you  some  account  of  certain  properties  of  electricity,  which 
have  of  late  yeais  been  discovered  to  have  an  essential  connec- 
tion with  the  phenomena  of  chemistry. 

Caroline.  It  is  FLECTRICITY,  if  I  recollect  right,  which  comes 
next  in  our  list  of  simple  substances  ? 

Mrs.  B.  I  have  placed  electricity  in  that  list,  rather  from 
the  necessity  of  <  lassing  it  somewhere,  than  from  any  convic- 
tion that  it  has  a  right  to  that  situation,  for  we  are  as  yet  so  igno- 
rant of  its  intimate  nature,  that  we  are  unable  to  determine,  not 
onlv  whether  it  is  simple  or  compound,  but  whether  it  is  in  fact 
a  rhaterial  agent ;  or,  as  Sir  H.  Davy  has  hinted,  whether  it 
may  not  be  merely  a  property  inherent  in  matter.  As,  howev- 
er, it  is  necessary  to  adopt  some  hypothesis  for  the  explanation 
of  the  discoveries  which  this  agent  has  enabled  us  to  make,  I 
have  chosen  the  opinion,  at  present  most  prevalent,  which  sup- 
poses the  existence  of  two  kinds  of  electricity,  distinguished  by 
the  names  of  positive  and  negative  electricity. 

Caroline.  Well,  I  must  confess,  I  do  not  feel  nearly  so  in- 
terested in  a  science  in  which  so  much  uncertainty  prevails,  as  in 
those  which  rest  upon  established  principles ;  I  never  was  fond 
of  electricity,  because,  however  beautiful  and  curious  the  phe- 
nomena it  exhibits  may  be,  the  theories,  by  which  they  were 
explained,  appeared  to  me  so  various,  so  obscure  and  inade- 
quate, that  1  always  remained  dissatisfied.  I  was  in  hopes 
that  the  new  discoveries  in  electricity  had  thrown  so  great  a 
light  on  the  subject,  that  every  thing  respecting  it  would  now 
shave  been  clearly  explained. 

Mrs.  B.  That  is  a  point  which  we  are  yet  far  from  having 
attained.  But,  in  spite  of  the  imperfection  of  our  theories,  you 
will  be  amply  repaid  by  the  importance  and  novelty  of  the  sub- 
iect.  The  number  of  new  facts  which  have  already  been  as- 

*  The  electricity  extricated  by  the  metals  is  commonly  called  Gn^ 
yftnism.  C- 


ELECTRO-CHEMISTRY. 


curtained,  and  the  immense  prospect  of  discovery  which  has 
lately  been  opened  to  us,  will,  I  hope,  ultimately  lead  to  a  per- 
fect elucidation  of  this  branch  of  natural  science  ;  but  at  pres- 
ent you  must  be  contented  with  studying  the  effects,  and  in 
some  degree  explaining  the  phenomena,  without  aspiring  to  a 
precise  knowledge  of  the  remote  cause  of  electricity. 

You  have  already  obtained  some  notions  of  -electricity  :  in 
our  present  conversation,  therefore,  I  shall  confine  myself  to 
that  part  of  the  science  which  is  of  late  discovery,  and  is  more 
particularly  connected  with  chemistry. 

It  was  a  trifling  and  accidental  circumstance  which  first  gave 
rise  to  this  new  branch  of  physical  science.  Galvani,  a  pro- 
fessor of  natural  philosophy  at  Bologna,  being  engaged  (about 
twenty  years  ago)  in  some  experiments  on  muscular  irritabili- 
ty, observed,  that  when  a  piece  of  metal  was  laid  on  the  nerve 
of  a  frog,  recently  dead,  whilst  the  limb  supplied  by  that  nerve 
rested  upon  seme  other  metal,  the  limb  suddenly  moved,  on  a 
communication  being  made  between  the  two  pieces  of  metal. 

Emily.  How  is  this  communication  made  ? 

Mrs.  tt.  Either  by  bringing  the  two  metals  into  contact,  or 
by  connecting  them  by  means  of  a  metallic  conductor.  But 
without  subjecting  a  frog  to  any  cruel  experiments,  I  can  easily 
make  you  sensible  of  this  kind  of  electric  action.  Here  is  a 
piece  of  zinc,  (one  of  the  metals  I  mentioned  in  the  list  of  ele- 
mentary bodies)  —  put  it  under  your  tongue,  and  this  piece  of 
silver  upon  your  tongue,  and  let  both  the  metals  project  a  little 
beyond  the  tip  of  the  tongue  —  very  well  —  now  make  the  pro- 
jecting parts  of  the  metals  touch  each  other,  and  you  will  in- 
stantly perceive  a  peculiar  sensation. 

Emily.  Indeed  I  did,  a  singular  taste,  and  I  think  a  degree 
of  heat  ;  but  I  can  hardly  describe  it. 

Mrs.  B.  The  action  of  these  two  pieces  of  metal  on  the 
tongue  is,  I  believe,  precisely  similar  to  that  made  on  the  nerve 
of  a  frog.  I  shall  not  detain  you  by  a  detailed  account  of  the 
theory  by  which  Galvani  attempted  to  explain  this  fact,  as  it 
was  soon  overturned  by  subsequent  experiments,  which  proved 
that  Galvanism  (the  name  this  new  power  had  obtained)  was 
nothing  more  than  electricity.  Galvani  supposed  that  the  vir- 
tue of  this  new  agent  resided  in  the  nerves  of  the  frog,  but  Vol- 
ta,  who  prosecuted  this  subject  with  much  greater  success, 
showed  that  the  phenomena  did  not  depend  on  the  organs  of  the 
frog,  but  upon  the  electrical  agency  of  the  metals,  which  is  ex- 
cited by  the  moisture  of  the  animal,  the  organs  of  the  frog  be- 
ing only  a  delicate  test  of  the  presence  of  electric  influence. 

Caroline.  I  suppose,  then,  the  saliva  of  the  mouth  answers 


ELECTRO-CHEMISTRY. 

the  same  purpose  as  the  moisture  of  the  frog,  in  exciting  tht 
electricity  of  the  pieces  of  silver  and  zinc  with  which  Emily 
tried  the  experiment  on  her  tongue. 

Mrs.  B.  Precisely.  It  does  not  appear,  however,  necessa- 
ry 'hat  the  fluid  used  for  this  purpose  should  be  of  an  animal 
nature.  Water,  and  acids  very  much  diluted  by  water,  are 
found  to  be  the  most  effectual  in  promoting  the  developement  of 
electricity  in  metals;  and,  accordingly,  the  original  apparatus 
which  Volta  first  constructed  for  this  purpose,  consisted  of  a 
pile  or  succession  of  plates  of  zinc  and  copper,  each  pair  of 
which  was  connected  by  pieces  of  cloth  or  paper  impregnated 
with  water;  arid  this  instrument,  from  its  original  inconvenient 
structure  and  limited  strength,  has  gradually  arrived  at  this 
present  state  of  poxver  and  improvement,  such  as  is  exhibited 
in  the  Voltaic  battery.  In  this  apparatus,  a  specimen  of  which 
you  see  before  you  (PLATE  VI  fig.  1.,)  the  plates  of  zinc  and 
copper  are  soldered  together  in  pairs,  each  pair  being  placed 
at  regular  distances  in  wooden  troughs  and  the  interstices  being 
filled  with  fluid. 

Caroline.  Though  you  will  not  allow  us  to  inquire  into  the  pre- 
cise cause  of  electricity,  may  we  not  ask  in  what  manner  the 
fluid  acts  on  the  metals  so  as  to  produce  it  ? 

Mrs.  B.  The  action  of  the  fluid  on  the  metals,  whether  wa- 
«er  or  acid  be  used,  is  entirely  of  a  chemical  nature*  But  wheth- 
er electricity  is  excited  by  this  chemical  action,  or  whether  it  is 
produced  by  the  contact  of  the  two  metals,  is  a  point  upon 
which  philosophers  do  not  yet  perfectly  agree. 

Emily.  But  can  the  mere  contact  of  two  metals,  without  any 
intervening  fluid,  produce  electricity  ? 

Mrs.  B.  Yes,  if  they  are  afterwards  separated.  It  is  an  es- 
tablished fact,  that  when  two  metals  are  put  in  contact,  and  af- 
terwards separated,  that  which  has  the  strongest  attraction  for 
oxygen  exhibits  signs  of  positive,  the  other  of  negative  electrici- 
ty- 

Caroline.  It  seems  then  but  reasonoble  to  infer  that  the  pow- 
er of  the  Voltaic  battery  should  arise  from  the  contact  of  the 
plates  of  zinc  and  copper. 

Mrs.  B.  It  is  upon  this  principle  that  Volta  and  Sir  H.  Da- 
vy explain  the  phenomena  of  the  pile ;  but  notwithstanding 
these  two  great  authorities,  many  philosophers  entertain  doubts 
on  the  truth  of  this  theory.  The  chief  difficulty  which  occurs 
in  explaining  the  phenomena  of  the  Voltaic  battery  on  this  prin- 
ciple, is,  that  two  such  plates  show  no  signs  of  different  states 
of  electricity  whilst  in  contact,  but  only  on  being  separated  af- 
ter contact.  Now  in  the  Voltaic  battery,  those  plates  that  are 


.  3 . 
a/  Machine. 


.&A  tie  Cylinder.^  the  Conductor.-^  fa Xtttfr..  -C  ^  Cfa'm. 


ELECTRO-CHEMISTRY.  77 

m  contact  always  continue  so,  being  soldered  together:  and 
they  cannot  therefore  receive  a  succession  of  charges.  Be- 
sides, it"  we  consider  the  mere  disturbance  of  the  balance  of 
electricity  by  the  contact  of  the  plates,  as  the  sole  cause  of  the 
production  of  Voltaic  electricity^  it  remains  to  be  explained  how 
this  disturbed  balance  becomes  an  inexhaustible  source  of  elec- 
trical energy,  capable  of  pouring  forth  a  constant  and  copious 
supply  of  electrical  fluid,  though  without  any  means  of  replen- 
ishing itself  from  other  sources.  This  subject,  it  must  be  own- 
ed, is  involved  rn  too  much  obscurity  to  enable  us  to  speak  very 
decidedly  in  favour  of  any  theory.  But,  in  order  to  avoid  per- 
plexing you  with  different  explanations,  I  shall  confine  myself 
to  one  which  appears  to  me  to  be  least  encumbered  with  difficul- 
ties, and  most  likely  to  accord  with  truth.* 

This  theory  supposes  the  electricity  to  be  excited  by  the  chem- 
ical action  of  the  acid  on  the  zinc ;  but  you  are  yet  such  novi- 
ces in  chemistry,  that  I  think  it  will  be  necessary  to  give  you 
some  previous  explanation  of  the  nature  of  this  action. 

All  rnetals  have  a  strong  attraction  for  oxygen,  and  this  ele- 
ment is  found  in  great  abundance  both  in  water  and  in  acids. 
The  action  of  the  diluted  acid  on  the  zinc  consists  therefore  in 
its  oxygen  combining  with  it,  and  dissolving  its  surface. 

Caroline.  In  the  same  manner  I  suppose  as  we  saw  an  acid 
dissolve  copper? 

Mrs.  B  Yes;  but  in  the  Voltaic  battery  the  diluted  acid  is 
not  strong  enough  to  produce  so  complete  an  effect ;  it  acts  on- 
ly on  the  surface  of  the  zinc,  to  which  it  yields  its  oxygen,  for- 
ming upon  it  a  film  or  crust,  which  is  a  compound  of  the  oxy- 
gen and  the  metal. 

Emily.  Since  there  is  so  strong  a  chemical  attraction  between 
oxygen  and  metals,  I  suppose  they  are  naturally  in  different 
states  of  electricity  ? 

Mrs.  B.  Yes;  it  appears  that  all  metals  are  united  with  the 
positive,  and  that  oxygen  is  the  grand  source  of  the  negative 
electricity. 

*  This  m.  de  of  explaining  the  phenomena  of  the  Voltaic  pile  is  call- 
ed the  chemical  theory  of  electricity,  because  it  ascribes  the  cause  of 
these  phenomena  to  certain  chemical  changes  which  take  place  during 
their  appearance.  The  mode  which  is  here  sketched  was  long  since 
suggested  hy  Dr.  Bostock,  who  has  lately  (1818)  published  "  An  Ac- 
count of  the  History  and  present  State  of  Galvanism ;"  which  con- 
tains a  fuller  and  more  complete  statement  01  his  opinions,  and  those  of 
other  writers  on  the  subject,  than  any  of  his  former  papers, 

8  * 


78  ELECTRO-CHEMhTItV, 

Caroline.  Does  not  then  the  acid  act  on  the  plates  of  cop- 
per, as  well  as  on  those  of  zinc  ?* 

Mrs.  B.  No  ;  for  though  copper  has  an  affinity  for  oxygen, 
it  is  less  strong  than  that  of  zinc ;  and  therefore  the  energy  of 
the  acid  is  only  exerted  upon  the  zinc. 

It  will  be  best,  I  believe,  in  order  to  render  the  action  of  the 
Voltaic  battery  more  intelligible,  to  confine  our  attention  at  first 
to  the  effect  produced  on  two  plates  only.  (PLATE  VI.  fig.  2.) 

If  a  plate  of  zinc  be  placed  opposite  to  one  of  copper,  or 
any  other  metal  less  attractive  of  oxygen,  and  the  space  between 
them  (suppose  of  half  an  inch  in  thickness,)  be  filled  with  an 
acid  or  any  fluid  capable  of  oxydating  the  zinc,  the  oxydated 
surface  will  have  its  capacity  for  electricity  diminished,  so  that 
a  quantity  of  electricity  will  be  evolved  from  that  surface. 
This  electricity  will  be  received  by  the  contiguous  fluid,  by 
which  it  will  be  transmitted  to  the  opposite  metallic  surface,  the 
copper,  which  is  not  oxydated,  and  is  therefore  disposed  to  re- 
ceive it;  so  that  the  copper  plate  will  thus  become  positive, 
whilst  the  zinc  plate  will  be  in  the  negative  state. 

This  evolution  of  electrical  fluid  however  will  be  very  limi- 
ted; for  as  these  two  plates  admit  of  but  very  little  accumula- 
tion of  electricity,  and  are  supposed  to  have  no  communication 
with  other  bodies,  the  action  of  the  acid,  and  further  develope- 
ment  of  electricity,  will  be  immediately  stopped. 

Emily.  This  action,  I  suppose,  can  no  more  continue  than 
that  of  a  common  electrical  machine,  which  is  not  allowed  to 
communicate  with  other  bodies? 

Mrs.  B.  Precisely ;  the  common  electrical  machine,  when 
excited  by  the  friction  of  the  rubber,  gives  out  both  the. positive 
and  negative  electricities. — (PLATE  VI.  Fig.  3.)  The  posi- 
tive, bv  the  rotation  of  the  glass  cylinder,  is  conveyed  into  the 
conductor,  whilst  the  negative  goes  into  the  rubber.  But^unless 
there  is  a  communication  made  between  the  rubber  and  the 
ground,  a  very  inconsiderable  quantity  of  electricity  can  be  ex- 
cited ;  for  the  rubber,  like  the  plates  of  the  battery,  has  too 
small  a  capacity  to  admit  of  an  accumulation  of  electricity. 
Unless  therefore  the  electricity  can  pass  out  of  the  rubber,  it 
will  not  continue  to  go  info  it,  and  consequently  no  additional 
accumulation  will  take  place.  JNow  as  one  kind  of  electricity 
cannot  be  given  out  without  the  other,  the  developement  of  the 
positive  electricity  is  stopped  as  well  as  that  of  the  negative, 

*  The  acid  acts  upon  the  copper,  but  not  so  strongly  as  on  the  zinc. 
Any  two  metals,  cue  of  which  nas  a  stronger  attraction  for  oxygen  than 
the  other,  will  form  the  galvanic  series.  C. 


feLEOTRO-CHEMISTRY".  7$ 

and  the  conductor  therefore  cannot  receive  a  succession  of  char- 
ges. 

Caroline.  But  does  not  the  conductor,  as  well  as  the  rubber, 
require  a  communication  with  the  earth,  in  order  to  get  rid  of 
its  electricity? 

Mrs.  B.  No;  for  it  is  susceptible  of  receiving  and  contain- 
ing a  considerable  quantity  of  electricity,  as  it  is  much  larger 
than  the  rubber,  and  therefore  has  a  greater  capacity;  and  this 
•continued  accumulation  of  electricity  in  the  conductor  is  what 
is  called  a  charge. 

Emily.  But  when  an  electrical  machine  is  furnished  with  two 
conductors  to  receive  the  two  electricities,  I  suppose  no  commu- 
nication with  the  earth  is  required  ? 

Mrs.  B.  Certainly  not,  until  the  two  are  fully  charged;  for 
the  two  conductors  will  receive  equal  quantities  of  electricity. 

Caroline.  I  thought  the  use  of  the  chain  had  been  to  convey 
the  electricity  from  the  ground  into  the  machine  ? 

Mrs.  B.  That  was  the  idea  of  Or.  Franklin,  who  supposed 
that  there  was  but  one  kind  of  electricity,  and  who,  by  the 
terms  positive  and  negative  (which  he  first  introduced,)  meant 
only  different  quantities  of  the  same  kind  of  electricity.*  The 
chain  was  in  that  case  supposed  to  convey  electricity />ow  the 
ground  through  the  rubber  into  the  conductor.  But  as  we  have 
adopted  the  hypothesis  of  two  electrics,  we  must  consider  the 
chain  as  a  vehicle  to  conduct  the  negative  electricity  into  the 
earth. 

Emily.  And  are  both  kinds  produced  whenever  electricity 
is  excited  ? 

Mrs.  B.  Yes,  invariably.  If  you  rub  a  tube  of  glass  with 
a  woolen  cloth,  the  glass  becomes  positive,  and  the  cloth  nega- 
tive.t  If,  on"  the  contrary,  you  excite  a  stick  of  sealing-wax 
by  the  same  means,  it  is  the  rubber  which  becomes  positive,  and 
the  wax  negative. 

*  The  idea  of  Dr.  Franklin,  was,  that  the  positive  state  consisted  iu 
the  presence,  or  accumulation  of  the  electric  fluid,  and  that  the  nega« 
tive  was  merely  its  absence  or  diminution.  Hence  the  terms  used  by 
him  to  indicate  these  states  ware  positive  and  negative.  In  this  chap- 
ter Mrs.  B.  has  used  these  terms  of  the  American  Philosopher  improp- 
erly, for  plus  and  minus  were  never  msant  to  signify  two  sorts  of  elec- 
tricity, but  only  its  presence,  or  absence.  Where  authors  have  adop* 
te<d  Dufay^  theory,  of  two  electricities,  thf-yhave  used  the,  terms,  vi- 
freous  and  resinous.  C. 

t  Most  probably,  because  the  glass  takes  the  electric  fluid  from  the 
cloth.  Indeed  we  conceive  there  is  about  the  same  reason  for  believing 
that  the;  negative  state,  is  the  absence  of  the  electric  fluid,  as  there  i? 
for  beliering  that  cold  is  the  absence  of  heat.  C. 


SO  ELECTRO-CHEMISTRY. 

But  with  regard  to  the  Voltaic  battery,  in  order  that  the  acid 
may  act  freely  on  the  zinc,  and  the  two  electricities  be  given 
out  without  interruption,  some  method  must  be  devised,  by 
which  the  plates  may  part  with  their  electricities  as  fast  as  they 
receive  them. — Can  you  think  of  any  means  by  which  this 
might  be  effected  ? 

Emily.  Would  not  two  chains  or  wires,  suspended  from  either 
plate  to  the  ground,  conduct  the  electricities  into  the  earth,  and 
thus  answer  the  purpose? 

Mrs.  B.  It  would  answer  the  purpose  of  carrying  off  the 
electricity,  I  admit ;  but  recollect,  that  though  it  is  necessary  to 
find  a  vent  for  the  electricity,  yet  we  must  not  lose  it,  since  it  is 
the  power  which  we  are  endeavouring  to  obtain.  Instead, 
therefore,  of  conducting  it  into  the  ground,  let  us  make  the 
wires,  from  either  plate,  meet:  the  two  electricities  will  thus 
be  brought  together,  and  will  combine  and  neutralize  each  oth- 
er; and  as  long  as  this  communication  continues,  the  two  plates 
having  a  vent  for  their  respective  electricities,  the  action  of  the 
acid  will  go  on  freely  and  uninterruptedly. 

Emily.  That  is  very  clear,  so  far  as  two  plates  only  are 
concerned  ;  but  1  cannot  say  I  understand  how  the  energy  of 
the  succession  of  plates,  or  rather  pairs  of  plates,  of  which 
the  Galvanic  trough  is  composed,  is  propagated  and  accumu- 
lated throughout  a  battery  ? 

JVIrs.  B.  In  order  to  show  you  how  the  intensity  of  the 
electricity  is  increased  by  increasing  the  number  of  plates,  we 
will  examine  the  action  of  four  plates;  if  you  understand  these, 
you  will  readily  comprehend  that  of  any  number  whatever. 
In  this  figure  (PLATE  VI.  fig.  4.,)  you  will  observe  'hat  the 
two  central  plates  are  united  ;  they  are  soldered  together,  (as 
we  observed  in  describing  the  Voltaic  trough,)  so  as  to  form 
but  one  plate  which  offers  two  different  surfaces,  the  one  of 
copper,  the  other  of  zinc. 

Now  you  recollect  that,  in  explaining  the  action  of  two  plates^ 
we  supposed  that  a  quantity  of  electricity  was  evolved  from 
the  surface  of  the  first  zinc  plate,  in  consequence  of  the  action 
of  the  acid,  and  was  conveyed  by  the  interposed  fluid  to  the 
copper  plate,  No.  2,  which  thus  became  positive.  This  cop- 
per plate  communicates  its  electricity  to  the  contiguous  zinc 
plate,  No.  3,  in  which,  consequently,  some  accumulation  of 
electricity  takes  place.  When,  therefore,  the  fluid  in  the  next 
cell  acts  upon  the  zinc  plate,  electricity  is  extricated  from  it  in 
larger  quantity,  and  in  a  more  concentrated  form  than  before. 
This  concentrated  electricity  is  again  conveyed  by  the  fluid  to 
the  next  pair  of  plates,  No.  4  and  5,  when  it  is  farther  increased 


ELECTRO-CHEMISTRY.  81 

by  the  action  of  the  fluid  in  the  third  cell,  and  so  on,  to  any 
number  of  plates  of  which  the  battery  may  consist  ;  so  that  the 
electrical  energy  will  continue  to  accumulate  in  proportion  to 
the  number  of  double  plates,  the  first  zinc  plate  of  the  series 
being  the  most  negative,  and  the  last  copper  plate  the  most 
positive. 

Caroline.  But  does  the  battery  become  more  and  more 
strongly  charged,  merely  bv  being  allowed  to  stand  undisturb- 
ed ? 

Mrs.  B.  No,  for  the  action  will  soon  stop,  as  was  explained 
before,  unless  a  vent  be  given  to  the  accumulated  electricities. 
This  is  easily  done,  however,  by  establishing  a  communication 
by  means  of  the  wires  (Fig.  1.,)  between  the  two  ends  of  the 
battery:  these  being  brought  into  contact,  the  two  electricities 
meet  and  neutralize  each  other,  producing  the  shock  and  other 
effects  of  electricity ;  and  the  action  goes  on  with  renewed 
energy,  being  no  longer  obstructed  by  the  accumulation  of  the 
two  electricities  which  impeded  its  progress, 

Emily.  Is  it  the  union  of  the  two  electricities  which  produ- 
ces the  electric  spark  ? 

Mrs.  B.  Yes ;  and  it  is,  I  believe,  this  circumstance  which 
gave  rise  to  Sir  H.  Davy's  opinion  that  caloric  may  be  a  com- 
pound of  the  two  electricities. 

Caroline.  Yet  surely  caloric  is  very  different  from  the  elec- 
trical spark  ? 

Mrs.  B.  The  difference  may  consist  probably  only  in  inten- 
sity ;  for  the  heat  of  the  electric  spark  is  considerably  more  in- 
tense, though  confined  to  a  very  minute  spot,  than  any  heat  we 
can  produce  by  other  means. 

Emily.  Is  it  quite  certain  that  the  electricity  of  the  Voltaic 
battery  is  precisely  of  the  same  nature  as  that  of  the  common 
electrical  machine  ? 

Mrs.  B.  Undoubtedly  ;  the  shock  given  to  the  human  body, 
the  spark,  the  circumstance  of  the  same  substances  which  are 
conductors  of  the  one  being  also  conductors  of  the  other,  and 
of  those  bodies,  such  as  glass  and  sealing-wax,  which  are  non- 
conductors of  the  one,  being:  also  non-conductors  of  the  other, 
are  striking  proofs  of  it.  Besides,  Sir  H.  Davy  has  shewn  in 
his  Lectures,  that  a  Leyden  jar,  and  a  common  electric  battery, 
can  be  charged  with  electricity  obtained  from  a  Voltaic  battery, 
the  effect  produced  being  perfectly  similar  to  that  obtained  by 
a  common  machine. 

Dr.  Wollaston  has  likewise  proved  that  similar  chemical  de- 
compositions are  effected  by  the  electric  machine  and  by  the 


82  ELECTRO-CHEMISTRY. 

Voltaic  battery;  and  has  made  other  experiments  which  ren- 
der it  highly  probable,  that  the  origin  of  both  electricities  is  es- 
sentially the  same,  as  they  show  thnt  the  rubber  of  the  common 
electrical  machine,  like  the  zinc  in  the  Vohaic  battery,  produces 
the  two  electricities  by  combining:  with  oxygen. 

Caroline.  But  I  do  not  see  whence  the  rubber  obtains  oxygen, 
for  there  is  neither  acid  nor  water  used  in  the  common  machine, 
and  I  always  understood  that  the  electricity  was  excited  by  the 
friction. 

Mrs.  B.  It  appears  that  by  friction  the  rubber  obtains  oxygen 
from  the  atmosphere,  which  is  partly  composed  of  that  ele- 
ment. The  oxygen  combines  with  the  amalgam  of  the  rubber, 
which  is  of  a  metallic  nature,  much  in  the  same  way  as  the 
oxygen  of  the  acid  combines  with  the  zinc  in  the  Voltaic  bat- 
tery, and  it  is  thus  that  the  two  electricities  are  disengaged. 

Caroline.  But,  if  the  electricities  of  both  machines  are  simi- 
lar, why  not  use  the  common  machine  for  chemical  decomposi- 
tion ? 

Mrs.  B.  Though  its  effects  are  similar  to  those  of  the  Voltaic 
battery,  they  are  incomparably  weaker.  Indeed  Dr.  Wollas- 
ton,  in  using  it  for  chemical  decompositions,  was  obliged  to 
act  upon  the  most  minute  quantities  of  matter,  and  though  the 
result  was  satisfactory  in  proving  the  similarity  of  its  effects  to 
those  of  the  Voltaic  battery,  these  effects  were  too  small  in  ex- 
tent to  be  in  any  considerable  degree  applicable  to  chemical  de- 
composition. 

Caroline.  How  terrible,  then,  the  shock  must  be  from  a 
Voltaic  battery,  since  it  is  so  much  more  powerful  than  an  elec- 
trical machine  ! 

Mrs.  B.  It  is  not  nearly  so  formidable  as  you  think  ;  at  least 
it  is  by  no  means  proportional  to  the  chemical  effect.  The 
great  superiority  of  the  Voltaic  battery  consists  in  the  large 
quantity  of  electricity  that  passes  ;  but  in  regard  to  the  rapidi- 
ty or  intensity  of  the  charge,  it  is  greatly  surpassed  by  the 
common  electrical  machine.  It  would  seem  that  the  shock  or 
sensation  depends  chiefly  upon  the  intensity  ;  whilst,  on  the 
contraiy,  for  chemical  purposes,  it  is  quantity  which  is  requi- 
red. In  the  Voltaic  battery,  the  electricity,  though  copious,  is 
so  weak  as  not  to  be  able  to  force  ?t->  way  through  the  fluid 
which  separates  the  plates,  whilst  that  of  a  common  roach;:  e 
will  pass  through  any  space  of  water. 

Caroline.  Would  not  it  be  possible  to  increase  the  intensi<y 
of  the  Voltaic  battery  till  it  should  equal  that  of  the  common 
machine  ? 

Mrs.  B.  It  can  actually  be  increased  till  it  imitates  a 


ELECTRO-CHEMISTRY.  83 

electrical  machine,  so  as  to  produce  a  visible  spark  when  accu- 
mulaied  in  a  Leyden  jar.  But  it  can  never  he  raised  sufficiently 
to  pa>»s  tliiongh  any  considerable  extent  of  air,  because  of  the 
ready  communication  through  the  fluids  employed. 

By  increasing  the  number  of  plates  of  a  battery,  you  in- 
crease its  intensity,  whilst,  by  enlarging  the  dimensions  of  the 
plates,  you  augment  its  quantity  ;  and,  as  the  superiority  of 
the  battery  over  the  common  machine  consists  entirely  in  the 
quantity  of  electricity  produced,  it  was  at  first  supposed  that  it 
was  the  size,  rather  than  the  number  of  plates  that  was  essen- 
tial to  the  augmentation  of  power.  It  was,  however,  found 
upon  trial,  that  the  quantity  of  electricity  produced  by  the 
Voltaic  battery,  even  when  of  a  very  moderate  size,  was  suffi- 
ciently copious,  and  that  the  chief •  advantage  in  this  apparatus 
was  obtained  by  increasing  the  intensity,  which,  however,  still 
falls  very  short  of  that  of  the  common  machine. 

1  should  not  omit  to  mention,  that  a  very  splendid,  and,  at 
the  same  time,  most  powerful  battery,  was,  a  few  years  ago, 
constructed  under  the  direction  of  Sir  H.  Davy,  which  he  re- 
peatedly exhibited  in  his  course  of  electro-chemical  lectures.  It 
consists  of  two  thousand  double  plates  of  zinc  and  copper,  of 
six  square  inches  in  dimensions,  arranged  in  troughs  of  Wedg- 
wood-ware, each  of  which  contains  twenty  of  these  plates. 
The  troughs  are  furnished  with  a  contrivance  for  lifting  the 
plates  out  of  them  in  a  very  convenient  and  expeditious  man- 
ner.* 

Caroline.  Well,  now  that  we  understand  the  nature  of  the 
action  of  the  Voltaic  battery,  I  long  to  hear  an  account  of  the 
discoveries  to  which  it  has  given  rise. 

Mrs.  B.  You  must  restrain  your  impatience,  my  dear,  for  I 
cannot  with  any  propriety  introduce  the  subject  of  these  disco- 
veries till  we  come  to  them  in  the  regular  course  of  our  studies. 
But,  as  almost  every  substance  in  nature  has  already  been  ex- 
posed to  the  influence  of  the  Voltaic  battery,  we  shall  very  soon 
have  occasion  to  notice  its  effects. 

*  A  model  of  this  mode  of  construction  is  exhibited  in  PLATE  XIII. 
Fig.  I. 

Note.  In  consequence  of  the  discoveries  of  Prof.  Hare,  of  Phila- 
delphia, the  present  theory  of  galvanism  must  probably  undergo  a 
radical  change.  This  gentleman  has  invented  a  new  method  of  extri- 
cating the  Voltaic  influence,  by  so  connecting  the  plates,  that  in  ef- 
fect only  two  great  surfaces  of  the  metals  are  presented  to  each  other. 
By  this  arrangement,  the  galvanic  action  on  different  substances,  has 
presented  some  new  phenomena.  The  calorific  principle  is  immensely 
increased,  while  the  electric  shock  is  hardly  to  be  perceived.  Prof, 
Hare  has  named  this  new  apparatus  caiorimotor,  or  heat  mover. 


$4  OXYGEN    AND    NITROGEN. 

CONVERSATION  VI. 
ON  OXYGEN  AND   NITROGEN. 
Mrs.  B.  TODAY  we  shall  examine  the  chemical  properties  oi 

the  ATMOSPHERE. 

Caroline.  I  thought  that  we  were  first  to  learn  the  nature  of 
OXYGEN,  which  conies  next  in  our  table  of  simple  bodies  ? 

Mrs.  B.  And  so  you  shall  5  the  atmosphere  being  composed 
of  two  principles,  OXYGEN  and  NITROGEN,  we  shall  proceed  to 
analyse  it,  and  consider  its  component  parts  separately. 

Emily.  I  always  thought  that  the  atmosphere  had  been  a  ve- 
ry complicated  fluid,  composed  of  all  the  variety  of  exhalations 
from  the  earth. 

Mrs.  B,  Such  substances  may  be  considered  rather  as  hetero- 
geneous and  accidental,  than  as  forming  any  of  its  component 
parts  ;  and  the  proportion  they  bear  to  the  whole  mass  is  quite 
inconsiderable. 

ATMOSPHERICAL  AIR  it  composed  of  two  gases,  known  by 
the  names  of  OXYGEN  GAS  and  NITROGEN  or  AZOTIC  GAS. 

Emily.  Pray  what  is  a  gas  ?* 

Mrs.  B.  The  name  of  gas  is  given  to  any  fluid  capable  of 
existing  constantly  in  an  aeriform  state,  under  the  pressure  and 
at  the  temperature  of  the  atmospheres 

Caroline.  Is  not  water,  or  any  other  substance,  when  evap- 
orated by  heat,  called  gas  ? 

Mrs.  B.  No,  my  dear ;  vapour  is,  indeed,  an  elastic  fluid, 
and  bears  a  strong  resemblance  to  a  gas  ;  there  are,  however, 
several  points  in  which  they  essentially  differ,  and  by  which 
you  may  always  distinguish  them.  Steam,  or  vapour,  owes 
its  elasticity  merely  to  a  high  temperature,  which  is  equal  to  that 
of  boiling  water.  And  it  differs  from  boiling  water  only  by 
being  united  with  more  caloric,  which,  as  we  before  explained, 
is  in  a  latent  state.  When  steam  is  cooled,  it  instantly  returns 
to  the  form  of  water;  but  air,  or  gas,  has  never  yet  been  ren- 
dered liquid  or  solid  by  any  degree  of  cold. 

The  new  views  which  he  has  been  induced  to  offer,  seem  to  be  confir- 
med by  the  action  ol'  the  colorimotor,  viz.  that  galvanism  is  a  com- 
pound of  electricity  and  caloric.  This  theory,  it  is  obvious,  will  set 
aside  many  of  the  principles  laid  down  in  the,  foregoing  chapter.  An 
account  of  this  theory,  with  a  description  of  the  calorimotor,  is  pub- 
lished in  ."•illiman's  Journal,  with  Observations  by  the  Editor  ;  also  in 
Hare's  edition  of  Henry  s  Chemistry.  C. 

*  All  kinds  of  air  differing  from  the  atmosphere,  are  called  by  this 
name.  C. 


OXYGEN  AND  NITROGEN.  &l< 

Emily.  But  does  not  gas,  as  well  as  vapour,  owe  its  elasticity 
to  caloric  ? 

Airs.  B.  It  was  the  prevailing  opinion ;  and  the  difference 
between  gas  and  vapour  was  thought  to  depend  on  the  different 
manner  in  which  caloric  was  united  with  the  bases  of  these  two 
kinds  of  elastic  fluids.  In  vapour  it  was  considered  as  in  a 
latent  state  ;  in  gas,  it  was  said  to  be  chemically  combined, 
But  the  late  researches  of  Sir  H.  Davy  have  given  rise  to  a  new 
theory  respecting  gases ;  and  there  is  now  reason  to  believe 
that  these  bodies  owe  their  permanently  elastic  state,  not  solely 
to  caloric,  but  likewise  to  the  prevalence  of  either  the  one  or  the 
other  of  the  two  electricities.* 

Emily.  When  you  speak,  then,  of  the  simple  bodies,  oxygen 
and  nitrogen,  you  mean  to  express  those  substances  which  are 
the  basis  of  the  two  gases  ? 

Mrs.  B.  Yes,  in  strict  propriety,  for  they  can  properly^be 
called  gases  only  when  brought  to  an  aeriform  state. 

Car(,line.  In  what  proportions  are  they  combined  in  the  at 
mosphere  ? 

Mrs.  B.  The  oxygen  gas  constitutes  a  little  more  than  one- 
fifth,  and  the  nitrogen  gas  a  little  less  than  four-fifths.t  When 
separated,  they  are  found  to  possess  qualities  totally  different 
from  each  other.  For  oxygen  gas  is  essential  both  to  respira- 
tion and  combustion,  while  neither  of  these  processes  can  be 
performed  in  nitrogen  gas. 

Caroline.  But  if  nitrogen  gas  is  unfit  for  respiration,  how 
does  it  happen  that  the  large  proportion  of  it  which  enters  into 
the  composition  of  the  atmosphere  is  not  a  great  impediment  to 
breathing  ? 

Mrs.  B.  We  should  breathe  more  freely  than  our  lungs  could 
bear,  if  we  respired  oxygen  gas  alone.  The  nitrogen  is  no  im- 
pediment to  respiration,  and  probably,  on  the  contrary,  answers 
some  useful  purpose,  though  we  do  not  know  in  what  manner  it 
acts  in  that  process. 

Emily.  And  by  what  means  ran  the  two  gases,  which  com- 
pose the  atmospheric  air  be  separated  ? 

Mrs.  B.  There  are  many  ways  of  analysing  the  atmosphere: 
the  two  gases  may  be  separated  first  by  combustion. 

*  This  wants  further  proof.  The  former  theory,  that  the  gases  owe 
their  elasticity  to  caloric  combined  with  their  bases,  we  think  accounts 
equally  well  for  this  property,  and  at  the  same  time  is  more  simple, 
and  better  proved.  C. 

t  In  100  parts  of  atmospheric  air,  there  is  21  of  oxygen  and  79  of 
nitrogen.  C. 

9 


36  OXYGEN    AND    NITROGEN. 

Emily.  You  surprise  me !  how  is  it  possible  that  combustion 
should  separate  them  ? 

J\.;rs.  b.  I  should  previously  remind  you  that  oxygen  is  sup- 
posed to  be  the  only  simple  body  naturally  combined  with  neg- 
ative electricity.  In  all  the  other  elements  the  positive  electri- 
city prevails,  and  they  have  consequently,  all  of  them,  an  at- 
traction for  oxygen.*  t 

Caroline.  Oxygen  the  only  negatively  electrified  body  !  that 
surprises  me  extremely  ;  how  then  are  the  combinations  of  the 
other  bodies  performed,  if,  according  to  your  explanation  of 
chemical  attraction,  bodies  are  supposed  only  to  combine  in 
virtue  of  their  opposite  states  of  electricity  ? 

Mrs.  B.  Observe  that  I  said,  that  oxygen  was  the  only  sim- 
ple body,  naturally  negative.  Compound  bodies,  in  which  ox- 
ygen prevails  over  the  other  component  parts,  are  also  nega- 
tive, but  their  negative  energy  is  greater  or  less  in  proportion 
as  the  oxygen  predominates.  Those  compounds  into  which 
oxygen  enters  in  less  proportion  than  the  other  constituents,  are 
positive,  but  their  positive  energy  is  diminished  in  propor- 
tion to  the  quantity  of  oxygen  which  enters  into  their  composi- 
tion. 

All  bodies,  therefore,  that  are  not  already  combined  with 
oxygen,  will  attract  it,  and,  under  certain  circumstances,  will 
absorb  it  from  the  atmosphere,  in  which  case  the  nitrogen  gas 
will  remain  alone,  and  may  thus  be  obtained  in  its  separate 
state. 

Caroline.  I  do  not  understand  how  a  gas  can  be  absorbed  ? 

Mrs.  B.  It  is  only  the  oxygen,  or  basis  of  the  gas,  which  is 
absorbed  ;  and  the  two  electricities  escaping,  that  is  to  say,  the 
negative  from  the  oxygen,  the  positive  from  the  burning  body, 
unite  and  produce  caloric. 

*  If  chlorine  or  oxymuriatic  gas  be  a  simple  body,  according  to  Sir 
H.  Davy's  view  of  the  subject,  it  must  be  considered  as  an  exception 
to  this  statement;  hut  this  suhject  cannot  be  discussed  till  the  proper- 
ties and  nature  of  chlorine  come  under  examination. 

t  the  hypothesis  that  combustion,  as  well  as  chemical  affinity  are 
electrical  phenomena,  was  first  proposed  by  Berzelius,  of  Stockholm. 
The  theory  is  shortly  this.  In  all  cases,  where  the  particles  of  bodies, 
have  a  chemical  attraction  for  each  other,  they  are  in  opposite  states 
of  electricity,  and  the  force  of  their  union  is  in  proportion  to  the  inten- 
sity of  these  electrical  states,  since  it  is  this  which  forces  them  te 
unite.  Thus  the  particles  of  an  acid,  and  an  alkali  unite,  because  one 
is  strongly  negative,  and  the  other  strongly  positive.  In  cases  of  com- 
bustion, these  different  states  are  still  more  intense,  oxygen  always  be- 
ing in  the  negative  state,  and  the  combustible  in  the  positive,  and  M'he» 
a  union  takes  place,  heat  and  lieht  is  the  consequence.  This  theory- 
is  not  well  proved,  nor  generally  adopted.  C. 


OXYGEN    AND   NITROGEN. 

Emily.  And  what  becomes  of  this  caloric  ? 

Mrs.  B.  We  shall  make  this  piece  of  dry  wood  attract  oxy- 
gen from,  the  atmosphere,  and  you  will  see  what  becomes  of  the 
caloric. 

Caroline.  You  are  joking,  Mrs.  B —  ;  you  do  not  mean  to 
decompose  the  atmosphere  with  a  piece  of  dry  stick  ? 

Mrs.  B.  Not  the  whole  body  of  the  atmosphere,  certainly  ; 
out  if  we  can  make  this  piece  of  wood  attract  any  quantity  of 
oxygen  from  it,  a  proportional  quantity  of  atmospherical  air 
will  be  decomposed. 

Caroline.  If  wood  has  so  strong  an  attraction  for  oxygen, 
why  does  it  not  decompose  the  atmosphere  spontaneously  ? 

Mrs.  B.  It  is  found  by  experience,  that  an  elevation  of  tem- 
perature is  required  for  the  commencement  of  the  union  of  the 
oxygen  and  the  wood. 

This  elevation  of  temperature  was  formerly  thought  to  be 
necessary,  in  order  to  diminish  the  cohesive  attraction  of  the 
wood,  and  enable  the  oxygen  to  penetrate  and  combine  with  it 
more  readily.  But  since  the  introduction  of  the  new  theory  of 
chemical  combination,  another  cause  has  been  assigned,  and  it 
is  now  supposed  that  the  high  temperature,  by  exalting  the  elec- 
trical energies  of  bodies,  and  consequently  their  force  of  attrac- 
tion, facilitates  their  combination. 

Emily.  If  it  is  true,  that  caloric  is  composed  of  the  two  elec- 
tricities, an  elevation  of  temperature  must  necessarily  augment 
the  electric  energies  of  bodies. 

Mrs.  B.  I  doubt  whether  that  would  be  a  necessary  conse- 
quence ;  for,  admitting  this  composition  of  caloric,  it  is  only  by 
fts  being  decomposed  that  electricity  can  be  produced.  Sir  H. 
Davy,  however,  in  his  numerous  experiments,  has  found  it  to  be 
an  almost  invariable  rule  that  the  electrical  energies  of  bodies  are 
increased  by  elevation  of  temperature. 

What  means  then  shall  we  employ  to  raise  the  temperature 
of  the  wood,  so  as  to  enable  it  to  attract  oxygen  from  the  atmos- 
phere ? 

Caroline.  Holding  it  near  the  fire,  I  should  think,  would  an- 
swer the  purpose. 

Mrs.  B.  It  may,  provided  you  hold  it  sufficiently  close  to 
the  fire ;  for  a  very  considerable  elevation  of  temperature  is  re- 
quired. 

Caroline.  It  has  actually  taken  fire,  and  yet  I  did  not  let  it 
touch  the  coals,  but  I  held  it  so  very  close  that  I  suppose  it 
caught  fire  merely  from  the  intensity  of  the  heat. 

'.  >5.  B  Or  you  might  say,  in  other  words,  that  the  caloric 
which  the  wood  imbibed,  so  much  elevated  its  temperature,  and 


38  OXYGEN    AND    NITROGEN. 

exalted  its  electric  energy,  as  to  enable  it  to  attract  oxygen  very 
rapidly  from  the  atmosphere. 

Emily.  Does  the  wood  absorb  oxygen  while  it  is  burning  ? 

Mrs.  B.  Yes,  and  the  heat  and  light  are  produced  by  the  un- 
ion of  the  two  electricities  which  are  set  at  liberty,  in  conse- 
quence of  the  oxygen  combining  with  the  wood. 

Caroline.  You  astonish  me !  the  heat  of  a  burning  body 
proceeds  then  as  much  from  the  atmospere  as  from  the  body 
itself? 

Mrs.  B.  It  was  supposed  that  the  caloric,  given  out  during 
combustion,  proceeded  entirely,  or  nearly  so,  from  the  decom- 
position of  the  oxygen  gas ;  but,  according  to  Sir  H.  Davy's 
new  view  of  the  subject,  both  the  oxygen  gas,  and  the  combus- 
tible body,  concur  in  supplying  the  heat  and  light,  by  the  union 
of  their  opposite  electricities. 

Emily.  1  have  not  yet  met  with  any  thing  in  chemistry  that 
has  surprised  or  delighted  me  so  much  as  this  explanation  of 
combustion.  I  was  at  first  wondering  what  connection  there 
could  be  between  the  affinity  of  a  body  for  oxygen  and  its  com- 
bustibility ;  but  I  think  I  understand  it  now  perfectly. 

Mrs.  B.  Combustion  then,  you  see,  is  nothing  more  than  the 
rapid  combination  of  a  body  with  oxygen,  attended  by  the  dis- 
engagement of  light  and  heat. 

Emily.  But  are  there  no  combustible  bodies  whose  attraction 
for  oxygen  is  so  strong,  that  they  will  combine  with  it,  without 
the  application  of  heat  ? 

Caroline.  That  cannot  be ;  otherwise  we  should  see  bodies 
burning  spontaneously. 

Mrs.  B.  But  there  are  some  instances  of  this  kind,  such  as 
phosphorus,  potassium,  and  some  compound  bodies,  which  I 
shall  hereafter  make  you  acquainted  with.  These  bodies,  how- 
ever, are  prepared  by  art,  for  in  general,  all  the  combustions 
that  could  occur  spontaneously,  at  the  temperature  of  the  at- 
mosphere, have  already  taken  place .5  therefore  new  combus- 
tions cannot  happen  without  the  temperature  of  the  body  being 
raised.  Some  bodies,  however,  will  burn  at  a  much  lower  tem- 
perature than  others. 

Caroline.  But  the  common  way  of  burning  a  body  is  not 
merely  to  approach  it  to  one  already  on  fire,  but  rather  to  put 
the  one  in  actual  contact  with  the  other,  as  when  I  burn  this 
piece  of  paper  by  holding  it  in  the  flame  of  the  fire. 

Mrs.  B.  The  closer  it  is  in  contact  with  the  source  of  caloric, 
the  sooner  wKl  its  temperature  be  raised  to  the  degree  necessary 
for  it  to  burn.  If  you  hold  it  near  the  fire,  the  same  effect  wilt 


1 


OXYGEN   AND   NITROGEN.  89 

be  produced  ;  but  more  time  will  be  required,  as  you  found  to 
be  the  case  with  the  piece  of  stick. 

Emily.  But  why  is  it  not  necessary  to  continue  applying  ca- 
loric throughout  th'.'  process  of  combustion,  in  order  to  keep  up 
the  electric  energy  of  the  wood,  which  is  required  to  enable  it  to 
combine  with  the  oxygen  ? 

Mrs.  B.  The  caloric  which  is  gradually  produced  by  the  two 
electricities  during  combustion,  keeps  up  the  temperature  of  the 
burning  body,  so  that  when  once  combustion  has  begun,  no 
further  application  of  caloric  is  required. 

Caroline.  Since  I  have  learnt  this  wonderful  theory  of  com- 
bustion, I  cannot  take  my  eyes  from  the  fire  ;  and  I  can  scarce- 
ly conceive  that  the  heat  and  light,  which  I  always  supposed  to 
proceed  entirely  from  the  coals,  are  really  produced  as  much 
by  the  atmosphere. 

Emily.  When  you  blow  the  fire,  you  increase  the  combustion, 
I  suppose,  by  suyplying  the  coals  with  a  greater  quantity  of 
oxygen  gas  ? 

Mrs.  B.  Certainly  ;  but  of  course  no  blowiug  will  produce 
combustion,  unless  the  temperature  of  the  coals  be  first  raised. 
A  single  spark,  however,  is  sometimes  sufficient  to  produce  that 
effect ;  for,  as  I  said  before,  when  once  combustion  has  com- 
menced, the  caloric  disengaged  is  sufficient  to  elevate  the  tem- 
perature of  the  rest  of  the  body,  provided  that  there  be  a  free 
access  of  oxygen.  It  however  sometimes  happens  that  if  a  fire 
be  ill  made,  it  will  be  extinguished  before  all  the  fuel  is  consum- 
ed, from  the  very  circumstance  of  the  combustion  being  so  slow 
that  the  caloric  disengaged  is  insufficient  to  keep  up  the  tempe- 
rature of  the  fuel.  You  must  recollect  that  there  are  three 
things  required  in  order  to  produce  combustion  ;  a  combustible 
body,  oxygen,  and  a  temperature  at  which  the  one  will  combine 
with  the  other. 

Emily.  You  said  that  combustion  was  one  method  of  decom- 
posing the  atmosphere,  and  obtaining  the  nitrogen  gas  in  its 
simple  state;  but  how  do  you  secure  this  gas5  and  prevent  it 
from  mixing  with  the  rest  of  the  atmosphere  ? 

Mrs.  B.  It  is  necessary  for  this  purpose  to  burn  the  body 
within  a  close  vessel,  which  is  easily  done. — We  shall  introduce 
a  small  lighted  taper,  (PLATE  VII.  Fig.  1.)  under  this  glass 
receiver,  which  stands  in  a  bason  over  water,  to  prevent  all 
communication  with  the  external  air.* 

'*  To  make  a  taper,  melt  some  bees  wax,  and  dip  into  it  a  strip  of 
cotton  cloth  about  ah  inch  wide,  and  before  it  is  cold,  twist  it  pretty 
hard.  Gotten  wick  does  better  than  the  cloth,  A  quart  tumbler make* 

9* 


90  OXYGEN   AND 

Caroline.  How  dim  the  light  burns  already !— It  is  now  ex- 
tinguished. 

Mrs.  B.  Can  you  tell  us  why  it  is  extinguished  ? 

Caroline.  Let  me  consider. — The  receiver  was  full  of  at- 
mospherical air  5  the  taper,  in  burning  within  it,  must  have 
combined  with  the  oxygen  contained  in  that  air,  and  the  caloric 
that  was  disengaged  produced  the  light  of  the  taper.  But  when 
the  whole  of  the  oxygen  was  absorbed,  the  whole  of  its  electrici- 
ty was  disengaged ;  consequently  no  more  caloric  could  be  pro- 
duced, the  taper  ceased  to  burn,  and  the  flame  was  extinguished. 

Mrs.  B.  Your  explanation  is  perfectly   correct. 

Emily.  The  two  constituents  of  the  oxygen  gas  being  thus 
disposed  of,  what  remains  under  the  receiver  must  be  pure  ni- 
trogen gas  ? 

Mrs.  B.  There  are  some  circumstances  which  prevent  the 
nitrogen  gas,  thus  obtained,  from  being  perfectly  pure  ;  but  we 
may  easily  try  whether  the  oxygen  has  disappeared,  by  putting 
another  lighted  taper  under  it. — You  see  how  instantaneously 
the  flame  is  extinguished,  for  want  of  oxygen  to  supply  the  ne- 
gative electricity  required  for  the  formation  of  caloric ;  and 
were  you  to  put  an  animal  under  the  receiver,  it  would  imme- 
diately be  suffocated.  But  that  is  an  experiment  which  I  do  not 
think  your  curiosity  will  tempt  you  to  try. 

Emily,  Certainly  not. — But  look  Mrs.  B.,  the  receiver  is  full 
of  a  thick  white  smoke.  Is  that  nitrogen  gas  ? 

Mrs.  />.  No,  my  clear  ;  nitrogen  gas  is  perfectly  transparent 
and  invisible,  like  common  air.  This  cloudiness  proceeds  from 
a  variety  of  exhalations,  which  arise  from  the  burning  taper, 
fhe  nature  of  which  you  cannot  yet  understand. 

Caroline.  The  water  within  the  receiver  has  now  risen  a  little 
above  its  level  in  the  bason.  What  is  the  reason  of  this  ? 

Mrs.  B.  With  a  moment's  reflection,  I  dare  say,  ^ou  would 
have  explained  it  yourself.  The  water  rises  in  consequence  of 
the  oxygen  gas  within  it  having  been  destroyed,  or  rather  de- 
composed by  the  combustion  of  the  taper. 

Caroline.  Then  why  did  not  the  water  rise  immediately 
when  the  oxygen  gas  was  destroyed? 

Mrs.  B.  Because  the  heat  of  the  taper,  whilst  burning,  pro- 
duced a  dilatation  of  the  air  in  the  vessel,  which  at  first  counter- 
acted this  effect. 

Another  means  of  decomposing  the  atmosphere  is  the  oxyge- 

A  good  receiver.  Two  or  three  inches  of  the  taper  can  be  fastened  to 
a  piece  of  wire,  bent  so  that  it  will  etand  up.  Thus  the  experiment  i* 
easily  made.  C, 


OXYGEN  AND   NITROGEN.  91 

nation  of  certain  metals.  This  process  is  very  analogous  to 
combustion  ;  it  is,  indeed,  only  a  more  general  term  to  express 
the  combination  of  a  body  with  oxygen. 

Caroline.  In  what  respeet,  then,  does  it  differ  from  combus- 
tion ? 

Mrs.  B.  The  combination  of  oxygen  in  combustion  is  always 
accompanied  by  a  disengagement  of  light  and  heat ;  whilst  this 
circumstance  is  not  a  necessary  consequence  of  simple  oxygen- 
ation. 

Caroline.  But  how  can  a  body  absorb  oxygen  without  the 
combination  of  the  two  electricities  which  produce  caloric  ? 

Mrs.  H.  Oxygen  does  not  always  present  itself  in  a  gaseous 
form  ;  it  is  a  constituent  part  of  a  vast  number  of  bodies,  both 
solid  and  liquid,  in  which  it  exists  in  a  state  of  greater  density 
than  in  the  atmosphere;  and  from  these  bodies  it  may  be  ob- 
tained without  much  disengagement  of  caloric.  It  may  like- 
wise, in  some  cases,  be  absorbed  from  the  atmosphere  without 
any  sensible  production  of  light  and  heat ;  for,  if  the  process 
be  slow,  the  caloric  is  disengaged  in  such  small  quantities,  and 
so  gradually,  that  it  is  not  capable  of  producing  either  light  or 
heat.  In  this  case  the  absorption  of  oxygen  is  called  oxygena- 
tion  or  oxydation,  instead  of  combustion,  as  the  production  of 
sensible  light  and  heat  is  essential  to  the  latter. 

Emily.  I  wonder  that  metals  can  unite  with  oxygen  ;  for,  as 
they  are  so  dense,  their  attraction  of  aggregation  must  be  very 
great ;  and  I  should  have  thought  that  oxygen  could  never  have 
penetrated  such  bodies. 

Airs.  B.  Their  strong  attraction  for  oxygen  counterbalances 
this  obstacle.  Most  metals,  however,  require  to  be  made  red- 
hot  before  they  are  capable  of  attracting  oxygen  in  any  consid- 
erable quantity.  By  this  combination  they  lose  most  of  their 
metallic  properties,  and  fall  into  a  kind  of  powder,  formerly 
called  calx,  but  now  much  more  properly  termed  an  oxyd  } 
thus  we  have  oxyd  of  lead,  oxyd  of  iron,  &c.* 

Emily.  And  in  the  Voltaic  battery,  it  is.  1  suppose,  an  oxyd 
«f  Zinc,  that  is  formed  by  the  union  of  the  oxygen  with  that 
metal  ? 

Mrs.  B.  Yes,  it  is. 

Caroline.  The  word  oxyd,  then,  simply  means  a  metal  com- 
bined with  oxygen  ? 

Mrs.  B.  Yes;  but  the  term  is  not  confined  to  metals,  though 
chiefly  applied  to  them.  Any  body  whatever,  that  has  combi- 
ned with  a  certain  quantity  of  oxygen,  either  by  means  of  oxy- 

*  Red  had  and  rust  of  iron,    C- 


02  OXYViEN   AND   NITROGEtf- 

dation  or  combustion,  is  called  an  oxyd,  and  is  said  to  be  oxydcf^ 
ted  or  oxygenated. 

Emily.  Metals,  when  converted  into  oxyds,  become,  I  sup- 
pose, negative  ? 

Mrs.  B.  Not  in  general ;  because  in  most  oxyds  the  positive 
energy  of  the  metal  more  than  counterbalances  the  native  en- 
ergy of  the  oxygen  with  which  it  combines. 

This  black  powder  is  an  oxyd  of  manganese,  a  metal  which 
has  so  strong  an  affinity  for  oxygen,  that  it  attracts  that  sub- 
stance from  the  atmosphere  at  any  known  temperature :  it  is 
therefore  never  found  in  its  metallic  form,  but  always  in  that  of 
an  oxyd,  in  which  state,  you  see,  it  has  very  little  of  the  appear, 
ance  of  a  metal.  It  is  now  heavier  than  it  was  before  oxyda. 
tion,  in  consequence  of  the  additional  weight  of  the  oxygen  with 
which  it  has  combined. 

Caroline.  I  am  very  glad  to  hear  that ;  for  I  confess  I  could 
not  help  having  some  doubts  whether  oxygen  was  really  a  sub- 
stance, as  it  is  not  to  be  obtained  in  a  simple  and  palpable  state  ; 
but  its  weight  is,  I  think,  a  decisive  proof  of  its  being  a  real 
body. 

J\!rs.  B.  It  is  easy  to  estimate  its  weight,  by  separating  it 
from  the  manganese,  and  finding  how  much  tho  latter  has  lost. 

Emily.  But  if  you  can  take  the  oxygen  from  the  metal,  shall  we 
not  then  have  it  in  its  palpable  simple  state  ? 

Airs.  B.  No  ;  for  I  can  only  separate  the  oxygen  from  the 
manganese,  by  presenting  to  it  some  other  body,  for  which  it 
has  a  greater  affinity  than  for  the  manganese.  Caloric.affording 
the  two  electricities  is  decomposed,  and  one  of  them  uniting 
with  the  oxygen,  restores  it  to  the  aeriform  state. 

Emily.  But  you  said  just  now,  that  manganese  would  attract 
oxygen  from  the  atmosphere  in  which  it  is  combined  with  the 
negative  electricity  ;  how,  therefore,  can  the  oxygen  have  a  su- 
perior affinity  for  that  electricity,  since  it  abandons  it  to  com- 
bine with  the  manganese  ? 

Mrs.  13.  I  give  you  credit  for  this  objection,  Emily  ;  and  the 
only  answer  I  can  make  to  it  is,  that  the  mutual  affinities  of  me- 
tals for  oxygen,  and  of  oxygen  for  electricity,  vary  at  different 
temperatures  ;  a  certain  degree  of  heat,  will,  therefore,  dispose 
a  metal  to  combine  with  oxygen,  whilst,  on  the  contrary,  the 
former  will  be  compelled  to  part  with  the  latter,  when  the  tem- 
perature is  further  increased.  I  have  put  some  oxyd  of  manga- 
nese into  a  retort,*  which  is  an  earthen  vessel  with  a  bent  neck, 

*"  To  collect  oxygen  gas,  take  an  oil  flask  and  having  fitted  a  cork 


0XYGEN    AND    NITROGEN. 

such  as  you  see  here.  (PLATE  VII.  Fig.  2.)  The  retort  con- 
taining the  manganese  you  cannot  see,  as  I  have  enclosed  it  in 
this  furnace,  where  it  is  now  red-hot.  But,  in  order  to  make 
you  sensible  of  the  escape  of  the  gas,  which  is  itself  invisible, 
I  have  connected  the  neck  of  the  retort  with  this  bent  tube,  the 
extremity  of  which  is  immersed  in  this  vessel  of  water. — 
(PLATE  VII.  Fig.  3.)  Do  you  seethe  bubbles  of  air  rise  through 
the  water  ? 

Caroline.  Perfectly.  This,  then,  is  pure  oxygen  gas;  what 
a  pity  it  shoujd  be  lost !  Could  you  not  preserve  it  ? 

Mrs.  B.  We  shall  collect  it  in  this  receiver.— For  this  pur- 
pose, you  observe,  I  first  fill  it  with  water,  ia  order  to  exclude 
the  atmospherical  air ;  and  then  place  it  over  the  bubbles  which 
issue  from  the  retort,  so  as  to  make  them  rise  through  the  water 
to  the  upper  part  of  the  receiver. 

Emily.  The  bubbles  of  oxygen  gas  rise,  I  suppose,  from 
their  specific  levity? 

Mrs.  B.  Yes;  for  though  oxygen  forms  rather  a  heavy  gas5 
it  is  light  compared  to  water.  You  see  how  it  gradually  displa- 
ces the  water  from  the  receiver.  It  is  now  f u  1  of  gas,  and  I 
may  leave  it  inverted  in  water  on  this  shelf,  where  I  can  keep 
the  gas  as  long  as  I  choose,  for  future  experiments.  This  ap- 
paratus (which  is  indispensable  in  all  experiments  in  which 
gasses  are  concerned)  is  called  a  water-bath.* 

Caroline.  It  is  a  very  clever  contrivance,  indeed  ;  equally 
simple  and  useful  How  convenient  the  shelf  is  for  the  receiver 
to  rest  upon  under  water,  and  the  holes  in  it  for  the  gas  to  pass 
into  the  receiver!  I  long  to  make  some  experiments  with  tins 
apparatus. 

Mrs.  /5.  I  shall  try  your  skill  that  way,  when  you  have  a  lit- 
tle more  experience.  I  am  now  going  to  show  you  an  experi- 
ment, which  proves,  in  a  very  striking  manner,  how  essential 
oxygen  is  to  combustion.  You  will  see  that  iron  itself  will 
burn  in  this  gas,  in  the  most  rapid  and  brilliant  manner. 

Caroline.  Really !  I  did  not  know  that  it  was  possible  t© 
burn  iron. 

to  it,  pierce  the  cork  so  as  to  admit  a  bent  glass  tube  ;  (the  bending 
is  done-over  a  spirit  lamp.)  Pus  into  the  fl^sk  some  black  oxyd  of  m  m- 
ganese,  and  pour  on  sulphuric  acid  enough  to  make  it  into  a  paste. 
Then  put  in  the  cork  and  tube,  and  having  connected  the  other  end  of 
the  tube  with  a  receiver,  in  the  tub  ot  water,  apply  the  heat  of  an  ar- 
gand  lamp.  C. 

*  A  common  large  sized  wash  tub,  with  a  board  4  or  5  inches  wide 
fixed  through  the  middle,  and  about  6  inches  from  the  top,  and  filled 
wit!i  water,  will  answer  very  well  lor  a  great  variety  of  experiments  on 
the  gases,  C, 


4  OXYGEN  AND  NITROGEN. 

Emily.  Iron  is  a  simple  body,  and  you  know,  Caroline,  that 
all  simple  bodies  are  naturally  positivej  and  therefore  must  have 
an  affinity  for  oxygen. 

Mrs.  B.  Iron  will,  however,  not  burn  in  atmospherical  air 
without  a  very  great  elevation  of  temperature  ;  but  it  is  eminent- 
ly combustible  in  pure  oxygen  gas  ;  and  what  will  surprise  you 
still  more,  it  can  be  set  on  fire  without  any  considerable  rise  of 
temperature.  You  see  this  spiral  iron  wire* — I  fasten  it  at  one 
end  to  this  cork,  which  is  made  to  fit  an  opening  at  the  top  of 
the  glass- receiver.  (PLATE  VII.  Fig.4.) 

Emily.  I  see  the  opening  in  the  receiver ;  but  it  is  carefully 
closed  by  a  ground  glass-stopper. 

Mrs.  B.  That  is  in  order  to  prevent  the  gas  from  escaping  ; 
but  I  shall  take  out  the  stopper,  and  put  in  the  cork,  to  which  the 
wire  hangs. — Now  I  mean  to  burn  this  wire  in  the  oxygen  gas, 
but  I  must  fix  a  small  piece  of  lighted  tinder  to  the  extremity  of 
it,  in  order  to  give  the  first  impulse  to  combustion  5  for,  howev- 
er powerful  oxygen  is  in  promoting  combustion,  you  must  re- 
collect that  it  cannot  take  place  without  some  elevation  of  tem- 
perature. I  shall  now  introduce  the  wire  into  the  receiver,  by 
quickly  changing  the  stoppers. 

Caroline.  Is  there  no  danger  of  the  gas  escaping  while  you 
change  the  stoppers  ? 

Mrs.  B.  Oxygen  gas  is  a  little  heavier  than  atmospherical 
air,  therefore  it  will  not  mix  with  it  very  rapidly;  and,  if  I  do 
not  leave  the  opening  uncovered,  we  shall  not  lose  any 

Caroline.  Oh,  what  a  brilliant  and  beautiful  flame  ! 

Emily.  It  is  as  white  and  dazzling  as  the  sun  ! — Now  apiece 
of  the  melted  wire  drops  to  the  bottom  :  I  fear  it  is  extinguish- 
ed ;  but  no,  it  burns  again  as  bright  as  ever. 

Mrs.  B.  It  will  burn  till  the  wire  is  entirely  consumed,  pro- 
vided the  oxygen  is  not  first  expended :  for  you  know  it  can 
burn  only  while  there  is  oxygen  to  combine  with  it. 

Caroline.  I  never  saw  a  more  beautiful  light.  My  eyes  cart 
hardly  bear  it !  How  astonishing  to  think  that  all  this  caloric 
was  contained  in  the  small  quantity  of  gas  and  iron  that  was 
enclosed  in  the  receiver ;  and  that,  without  producing  any  sen- 
sible heat ! 

Emily.  How  wonderfully  quick  combustion  goes  on  in  pure 

•*  The  combustion  of  steel,  as  a  watch  spring,  is  ranch  more  vivid 
than  that  of  iron.  This  affords  a  very  beautiful  experiment,  and  is 
easily  made  aftvrthe  oxygen  is  collected.  A  bottle  of  white  glass  of  a 
. A  n...  j ii  «„  «  -«,,,->;„„,.  loch  of  water  at  the  bot- 


quart  capacity  does  well  as  a  receiver, 
torn  will  prevent  its  breaking.    C. 


OXYGEN   AND   NITROGEN.  $5 

oxygen  gas  !     But  pray,  are  these  drops  of  burnt  iron  as  heavy 
as  the  wire  was  before  ? 

Mrs.  B.  They  are  even  heavier ;  for  the  iron,  in  burning,  has 
acquired  exactly  the  weight  of  the  oxygen  which  has  disap- 
peared, and  is  now  combined  with  it.  it  has  become  an  oxyd 
of  iron. 

Caroline.  I  do  not  know  what  you  mean  by  saying  that  the 
oxygen  has  disappeared,  Mrs.  B.,  for  it  was  always  invisible. 

Mrs.B.  True,  my  dear;  the  expression  was  incorrect.  But 
though  you  could  not  see  the  oxygen  gas,  1  believe  you  had 
no  doubt  of  its  presence,  as  the  effect  it  produced  on  the  wire 
was  sufficiently  evident. 

Caroline.  Yes,  indeed  ;  yet  you  know  it  was  the  caloric,  and 
not  the  oxygen  gas  itself,  that  dazzled  us  so  much. 

Mrs.  B.  You  are  not  quite  correct  in  your  turn,  in  saying 
the  caloric  dazzled  you ;  for  caloric  is  invisible ;  it  affects  only 
the  sense  of  feeling;  it  was  the  light  which  dazzled  you. 

Caroline.  True ;  but  light  and  caloric  are  such  constant  com- 
panions, that  it  is  difficult  to  separate  them,  even  in  idea. 

Mrs.  B.  The  easier  it  is  to  confound  them,  the  more  careful 
you  should  be  in  making  the  distinction. 

Caroline.  But  why  has  the  water  now  risen,  and  filled  part 
of  the  receiver? 

Airs.  B.  Indeed,  Caroline,  I  did  not  suppose  you  would  have 
asked  such  a  question  !  I  dare  say,  Emily,  you  can  answer  it. 

Emily.  Let  me  reflect The  oxygen  has  combined 

with  the  wire;  the  caloric  has  escaped  ;  consequently  nothing 
can  remain  in  the  receiver,  and  the  water  will  rise  to  fill  the 
vacuum. 

Caroline.  I  wonder  that  I  did  not  think  of  that.  I  wish 
that  we  had  weighed  the  wire  and  the  oxygen  gas  before  co  n- 
bustion  ;  we  might  then  have  found  whether  the  weight  of  the 
oxyd  was  equal  to  that  of  both.  , 

Mrs.  B.  You  might  try  the  experiment  if  you  particularly 
wished  it ;  but  I  can  assure  you,  that,  if  accurately  performed, 
it  never  fails  to  show  that  the  additional  weight  of  the  oxyd  is 
precisely  equal  to  that  of  the  oxygen  absorbed,  whether  the  pro- 
cess has  been  a  real  combustion,  or  a  simple  oxygenation. 

Caroline.  But  this  cannot  be  the  case  with  combustions  in 
goneral;  for  when  any  substance  is  burnt  in  the  common  air, 
so  far  from  increasing  in  weight,  it  is  evidently  diminished,  and 
sometimes  entirely  consumed. 

Mrs.  B.  But  what  do  you  mean  by  the  expression  consumed? 
You  cannot  suppose  that  the  smallest  particle  of  any  substance 
in  nature  can  be  actually  destroyed.  A  compound  body  is  de* 


96  OXYGEN   AND   NITROGEN. 

composed  by  combustion ;  some  of  its  constituent  parts  fly  oil 
in  a  gaseous  form,  while  others  remain  in  a  concrete  state ;  the 
former  are  called  the  volatile,  the  latter  the  fixed  products  oi 
combustion.  But  if  we  collect  the  whole  of  them,  we  shall 
always  find  thnt  they  exceed  the  weight  of  the  combustible  bo- 
dy, by  that  of  the  oxygen  which  has  combined  with  them  du- 
ring combustion. 

Emily.  In  the  combustion  of  a  coal  fire,  then^I  suppose  that 
the  ashes  are  what  would  be  called  the  fixed  product,  and  the 
smoke  the  volatile  product? 

Mrs.  B.  Yet  when  the  fire  burns  best,  and  the  quantity  of 
volatile  products  should  be  the  greatest,  there  is  no  smoke;  how 
can  you  account  for  that  ? 

Emily  Indeed  I  cannot ;  therefore  I  suppose  that  I  was  not 
right  in  my  conjecture. 

Mrs.  B.  Not  quite;  ashes,  as  you  supposed,  are  a  fixed  pro- 
duct of  combustion  ;  but  smoke,  properly  speaking,  is  not  one 
of  the  volatile  products,  as  it  consists  of  some  minute  undecom- 
posed  particles  of  the  coals  which  are  carried  off  by  the  heat- 
ed air  without  being  burnt,  and  are  either  deposited  in  the  form 
of  soot,  or  dispersed  by  the  wind.  Smoke,  therefore,  ultimate- 
ly, becomes  one  of  the  fixed  products  of  combustion.  And 
you  may  easily  conceive  that  the  stronger  the  fire  is,  the  less 
smoke  is  produced,  because  the  fewer  particles  escape  combus- 
tion. On  this  principle  depends  the  invention  of  Argand's 
Patent  Lamps;  a  current  of  air  is  made  to  pass  through  the 
cylindrical  wick  of  the  lamp,  by  which  means  it  is  so  plentiful- 
ly supplied  with  oxygen,  that  scarcely  a  particle  of  oil  escapes 
combustion,  nor  is  there  any  smoke  produced. 

Emily.  But  what  then  are  the  volatile  products  of  combus- 
tion ? 

Mrs.  B.  Various  new  compounds,  with  which  you  are  not 
yet  acquainted,  and  which  being  converted  by  caloric  either  in- 
to vapour  or  gas,  are  invisible ;  but  they  can  be  collected,  and 
we  shall  examine  them  at  some  future  period. 

Caroline.  There  are  then  other  gases,  besides  the  oxygen 
and  nitrogen  gases. 

Mrs.  B.  Yes,  several :  any  substance  that  can  assume  and 
maintain  the  form  of  an  elastic  fluid  at  the  temperature  of  the 
atmosphere,  is  called  a  gas.  We  shall  examine  the  several 
gases  in  their  respective  places  :  but  we  must  now  confine  our 
attention  to  those  which  compose  the  atmosphere. 

I  shall  show  you  another  method  of  decomposing  the  atmos- 
phere, which  is  very  simple.  In  breathing,  we  retain  a  portion 
of  the  oxygen,  and  expire  the  nitrogen  gas ;  so  that  if  we  breathe 


OXYGEN   AND   NITROGEN.  97 

in  a  closed  vessel,  for  a  certain  length  of  time,  the  air  within  it 
will  be  deprived  of  its  oxygen  gas.  Which  of  you  will  make 
the  experiment  ? 

Caroline.  I  should  be  very  glad  to  try  it. 

Mrs.  B.  Very  well ;  breathe  several  times  through  this  glass 
tube  into  the  receiver  with  which  it  is  connected,  until  you  feel 
that  your  breath  is  exhausted. 

Caroline.  I  am  quite  out  of  breath  already  1 

Mrs.  B.  Now  let  us  try  the  gas  with  a  lighted  taper. 

Emily.  It  is  very  pure  nitrogen  gas,  for  the  taper  is  immedi- 
ately extinguished. 

Mrs.  B.  That  is  not  a  proof  of  its  being  pure,  but  only  of  the 
absence  of  oxygen,  as  it  is  that  principle  alone  which  can  pro- 
duce combustion,  every  other  gas  being  absolutely  incapable  of 
it.* 

Emily.  In  the  methods  which  you  have  shown  us,  for  decom- 
posing the  atmosphere,  the  oxygen  always  abandons  the  nitro- 
gen; but  is  there  no  way  of  taking  the  nitrogen  from  the  oxy- 
gen, so  as  to  obtain  the  latter  pure  from  the  atmosphere  ? 

Mrs.  B.  You  must  observe,  that  whenever  oxygen  is  taken 
from  the  atmosphere,  it  is  by  decomposing  the  oxygen  gas;  we 
cannot  do  the  same  with  the  nitrogen  gas,  because  nitrogen  has 
a  stronger  affinity  for  caloric  than  for  any  other  known  princi- 
ple :  it  appears  impossible  therefore  to  separate  it  from  the  at- 
mosphere by  the  power  of  affinities.  But  if  we  cannot  obtain 
the  oxygen  gas,  by  this  means,  in  its  separate  state,  we  have  no 
difficulty  (as  you  have  seen)  to  procure  it  in  its  gaseous  form, 
by  taking  it  from  those  substances  that  have  absorbed  it  from 
the  atmosphere,  as  we  did  with  the  oxyd  of  manganese. 

Emily.  Can  atmospherical  air  be  recom posed,  by  mixing 
due  proportions  of  oxygen  and  nitrogen  gases  ? 

Mrs.  B.  Yes :  if  about  one  part  of  oxygen  gas  be  mixed  with 
about  four  parts  of  nitrogen  gas,  atmospherical  air  is  produ- 
ced.t 

Emily.  The  air,  then,  must  be  an  oxyd  of  nitrogen  ? 

Mrs.  B.  No,  my  dear ;  for  it  requires  a  chemical  combina- 
tion between  oxygen  and  nitrogen  in  order  to  produce  an  ox- 
yd; whilst  in  the  atmosphere  these  two  substances  are  separate- 
ly combined  with  caloric,  forming  two  distinct  gases,  which 
are  simply  mixed  in  the  formation  of  the  atmosphere. 

I  shall  say  nothing  more  of  oxygen  and  nitrogen  at  present, 

*  This  does  not  a^ree  with  the  opinion  that  chlorine,  and  iodine  are 
simple  bodies,  since  they  are  both  supporters  of  combustion."  C. 

t  The  proportion  of  oxygen  in*  the  atmosphere  varies  from  21  to  22 
per  cent, 

10 


98  HYDRO GEN. 

as  we  shall  continually  have  occasion  to  refer  to  them  in  our 
future  conversations.  They  are  both  very  abundant  in  nature ; 
nitrogen  is  the  most  plentiful  in  the  atmosphere,  and  exists  also 
in  all  animal  substances;  oxygen  forms  a  constituent  part,  both 
of  the  animal  and  vegetable  kingdoms,  from  which  it  may  be 
obtained  by  a  variety  of  chemical  means.  But  it  is  now  time  to 
conclude  our  lesson.  I  am  afraid  you  have  learnt  more  to-day 
than  you  will  be  able  to  remember. 

Caroline.  I  assure  you  that  I  have  been  too  much  interested 
in  it,  ever  to  forget  it.  In  regard  to  nitrogen  there  seems  to  be 
but  little  to  remember;  it  makes  a  very  insignificant  figure  in 
cor  p  \rison  to  oxygen,  although  it  composes  a  much  larger  por- 
tion of  the  atmosphere. 

Mrs.  i~j.  Perhaps  this  insignificance  you  complain  of  may 
arise  from  the  compound  nature  of  nitrogen,  for  though  I  have 
hitherto  considered  it  as  a  simple  body,  because  it  is  not  known 
in  any  natural  process  to  be  decomposed,  yet  from  some  exper- 
iments of  Sir  H.  Davy, there  appears  to  be  reason  for  suspecting 
that  nitrogen  is  a  compound  body  as  we  shall  see  afterwards. 
But  even  in  its  simple  state,  it  will  not  appear  so  insignificant 
when  you  are  better  acquainted  with  it ;  for  though  it  seems  to 
perform  but  a  passive  part  in  the  atmosphere,  and  has  no  very 
striking  properties,  when  considered  in  its  separate  state,  yet 
you  will  see  by-and  bye  what  a  very  important  agent  it  becomes, 
when  combined  witli  other  bodies.  But  no  more  of  this  at  pres- 
ent; we  must  reserve  it  for  its  proper  place. 


CONVERSATION  VII. 

ON  HYDROGEN. 

Caroline.  THE  next  simple  bodies  we  come  to  are  CHLORINE, 
and  IODINE.  Pray  what  kinds  of  substances  are  these;  are 
they  also  invisible  ? 

Mrs.  B.  No  ;  for  chlorine,  in  the  state  of  gas,  has  a  distinct 
greenish  colour,  and  is  therefore  visible ;  and  iodine,  in  the  same 
state,  has  a  beautiful  claret-red  colour.  The  knowledge  of  these 
two  bodies,  however,  and  the  explanation  of  their  properties, 
imply  various  considerations,  which  you  would  not  yet  be  able 
to  understand  ;  we  shall  therefore  defer  their  examination  to 
some  future  conversation,  and  we  shall  pass  on  to  the  next  sim- 
ple substance,  HYDROGEN,  which  we  cannot,  any  more  than  ox- 
ygen, obtain  in  a  visible  or  palpable  form.  We  are  acquainted 


HYDROGEN. 

with  it  only  In  its  gaseous  state,  as  we  are  with  oxygen  and  nK 
trogen. 

Caroline.  But  in  its  gaseous  state  it  cannot  be  called  a  sim- 
ple substance,  since  it  is  combined  with  heat  and  electricity  ? 

Mrs.  B.  True,  my  dear  ;  but  as  we  do  not  know  in  nature  of 
any  substance  which  is  not  more  or  less  combined  with  caloric 
and  electricity,  we  are  apt  to  say  that  a^substance  is  in  its  pure 
state  when  combined  with  those  agents  only. 

Hydrogen  was  formerly  called  inflammable  air,  as  it  is  ex- 
tremely combustible,  and  burns  with  a  great  flame.  Since  the 
invention  of  the  new  nomenclature,  it  has  obtained  the  name  of 
hydrogen,  which  is  derived  from  two  Greek  words,  the  meaning 
of  which  is  to  produce  water. 

Emily.  And  how  does  hydrogen  produce  water  ? 
Mrs.  B.  By  its  combustion.     Water  is  composed  of  eighty- 
nve  parts,  by  weight,  of  oxygen,  combined  with  fifteen  parts  of 
hydrogen ;  or  of  two  parts,  by  bulk  of  hydrogen  gas,  to  one 
part  of  oxygen  gas. 

Caroline.  Really  !  is  it  possible  that  water  should  be  a  com- 
bination  of  two  gases,  and  that  one  of  these  should  be  inflamma- 
ble air !  Hydrogen  must  be  a  most  extraordinary  gas  that  wiU 
produce  both  fire  and  water- 

Emily.  But  I  thought  you  said  that  combustion  could  take 
place  in  no  gas  but  oxygen  ? 

Mrs.  B.  Do  you  recollect  what  the  process  of  combustion 
consists  in  ? 

Emily.  In  the  combination  of  a  body  with  oxygen,  with  dis- 
engagement of  light  and  heat. 

Mrs.  B.  Therefore  when  I  say  that  hydrogen  is  combustible, 
I  mean  that  it  has  an  affinity  for  oxygen ;  but,  like  all  other 
combustible  substances,  it  cannot  burn  unless  supplied  with  ox- 
ygen, and  also  heated  to  a  proper  temperature. 

Caroline.  The  simply  mixing  fifteen  parts  of  hydrogen,  with 
eighty-five  parts  of  oxygen  gas,  will  not,  therefore,  produce 
water  ? 

Mrs.  B.  No  ;  water  being  a  much  denser  fluid  than  gases, 
in.  order  to  reduce  these  gases  to  a  liquid,  it  is  necessary  to  di- 
minish the  quantity  of  caloric  or  electricity  which  maintains 
them  in  an  elastic  form. 

Emily.  That  I  should  think  might  be  done  by  combining  the 
oxygen  and  hydrogen  together;  for  in  combining  they  would 
give  out  their  respective  electricities  in  the  form  of  caloric,  arid 
by  this  means  would  be  condensed. 

Caroline.  But  you  forget,  Emily,  that  in  order  to  make  the 
oxygen  and  hydrogen  combine,  you  must  begin  by  elevating 


100  HYDROGEN.' 

their  temperature,  which  increases,  instead  of  diminishing,  then 
electric  energies. 

Mrs.  B.  Emily  is,  however,  right;  for  though  it  is  necessary 
to  raise  their  temperature,  in  order  to  make  them  combine,  as 
that  combination  affords  them  the  means  of  parting  with  their 
electricities,  it  is  eventually  the  cause  of  the  diminution  of 
electric  energy. 

Caroline.  You  love  to  deal  in  paradoxes  to-day,  Mrs.  B.— - 
Fire,  then,  produces  water  ? 

Mrs.  B.  The  combustion  of  hydrogen  gas  certainly,  does  5 
but  you  do  not  seem  to  have  remembered  the  theory  of  com- 
bustion so  well  as  you  thought  you  would.  Can  you  tell  me 
what  happens  in  the  combustion  of  hydrogen  gas  ? 

Caroline.  The  hydrogen  combines  with  the  oxygen,  and 
their  opposite  electricities  are  disengaged  in  the  form  of  caloric. 
— Yes,  I  think  I  understand  it  now — by  the  loss  of  this  caloric, 
the  gases  are  condensed  into  a  liquid. 

Emily.  Water,  then,  I  suppose,  when  it  evaporates  and  in- 
corporates with  the  atmosphere,  is  decomposed  and  converted 
into  hydrogen  and  oxygen  gases  ? 

Mrs.  B.  No.  my  dear — there  you  are  quite  mistaken ;  the 
decomposition  of  water  is  totally  different  from  its  evapora- 
tion ;  for  in  the  latter  case  (as  you  should  recollect)  water  is  on- 
ly in  a  state  of  very  minute  division;  and  is  merely  suspended 
in  the  atmosphere,  without  any  chemical  combination,  and  with- 
out any  separation  of  its  constituent  parts.  As  long  as  these 
remain  combined,  they  form  W\TER,  whether  in  a  state  of  li- 
quidity, or  in  that  of  an  elastic  fluid,  as  vapour,  or  under  the 
solid  form  of  ice. 

[n  our  experiments  on  latent  heat,  you  may  recollect  that  we 
caused  water  successively  to  pass  through  these  three  forms, 
merely  by  an  increase  or  diminution  of  caloric,  without  employ- 
ing any  power  of  attraction,  or  effecting  any  decomposition. 

Caroline.  But  are  there  no  means  of  decomposing  water  ? 

Mrs.  B.  Yes,  several;  charcoal,  and  metals,  when  heated 
red  hot,  will  attract  the  oxygen  from  water,  in  the  same  manner 
as  they  will  from  the  atmosphere. 

Caroline.  Hydrogen,  I  see,  is  like  nitrogen,  a  poor  dependent 
friend  of  oxygen,  which  is  continually  forsaken  for  greater  fa- 
vourites. 

Mrs.  B.  The  connection,  or  friendship,  as  you  choose  to  call 
it,  is  much  more  intimate  between  oxygen  and  hydrogen,  in  the 
state  of  water,  than  between  oxygen  and  nitrogen,  in  the  atmos- 
phere ;  for,  in  the  first  case,  there  is  a  chemical  union  and  con- 
densation of  the  two  substances  5  in  the  latter,  they  are  simply 


HY&R6GEN.  101 

mixer!  together  in  their  gaseous  state.  You  will  find,  however, 
that,  in  some  cases,  nitrogen  is  quite  as  intimately  connected 
with  oxygen,  as  hydrogen  is. — But  this  is  foreign  to  our  present 
subject. 

Emily.  Water,  then,  is  an  oxyd,  though  the  atmospherical 
air  is  not  ? 

Mr*.  B.  It  is  not  commonly  called  an  oxyd,  though,  accor- 
ding to  our  definition,  it  may,  no  doubt,  be  referred  to  that  class 
of  bodies. 

Caroline.  I  should  like  extremely  to  see  water  decomposed. 

Mrs.  B.  I  can  gratify  your  curiosity  by  a  much  more  easy 
process  than  the  oxydation  of  charcoal  or  metals :  the  decom- 
position of  water  by  these  latter  means  take  up  a  great  deal  of 
time,  and  is  attended  with  much  trouble ;  for  it  is  necessary  that 
the  charcoal  or  metal  should  be  made  red  hot  in  a  furnace,  that 
the  water  should  pass  over  the.Ti  in  a  state  of  vapour,  that  the 
gas  formed  should  be  collected  over  the  water  bath,  &c.  In 
short,  it  is  a  very  complicated  affair.  But  the  same  effect  may 
be  produced  with  the  greatest  facility,  by  the  action  of  the 
Voltaic  battery,  which  this  will  give  me  an  opportunity  of  ex- 
hibiting. 

Caroline.  I  am  very  glad  of  that,  for  I  longed  to  see  the 
power  of  this  apparatus  in  decomposing  bodies. 

Mrs.  B.  For  this  purpose  I  fill  this  piece  of  glass-tube 
(PLATE  VIIL  Fig.  1.)  with  water,  and  cork  it  up  at  both  ends; 
through  one  of  the  corks  I  introduce  that  wire  of  the  battery 
which  conveys  the  positive  electricity  ;  and  the  wire  whick  con- 
veys the  negative  electricity  is  made  to  pass  through  the  other 
cork,  so  that  the  two  wires  approach  each  other  sufficiently 
near  to  give  out  their  respective  electricities. 

Caroline.  It  does  not  appear  to  me  that  you  approach  the 
wires  so  near  as  you  did  when  you  made  the  battery  act  by  it* 
self. 

Mrs.  B.  Water  being  a  better  conductor  of  electricity  than 
air,  the  two  wires  will  act  on  each  other  at  a  greater  distance  in 
the  former  than  in  the  latter. 

h/mily.  Now  the  electrical  effect  appears  :  I  see  small  bub- 
bles of  air  emitted  from  each  wire. 

Mrs.  B.  Each  wire  decomposes  the  water,  the  positive  hy 
combining  with  its  oxygen  which  is  negative,  the  negative  by 
combining  with  its  hydrogen  which  is  positive. 

Caroline.  That  is  wonderfully  cuiious  !  But  what  are  the 
small  bubbles  of  air  ? 

«V/rs.  B.  Those  that  appear  to  proceed  from  the  positive 
wire,  are  the  result  of  the  decomposition  of  the  water  by  that 

10* 


102  HYDROGEN. 

wire.  That  is  to  say,  the  positive  electricity  having  combined 
with  some  of  the  oxygen  of  the  water,  the  particles  of  hydro- 
gen which  were  combined  with  that  portion  of  oxygen  are  set  at 
liberty,  and  appear  in  the  form  of  small  bubbles  of  gas  or  air. 

Emily.  And  I  suppose  the  negative  fluid  having  in  the  same 
manner  combined  with  some  of  the  hydrogen  of  the  water,  the 
particles  of  oxygen  that  were  combined  with  it,  are  set  free,  and 
emitted  in  a  gaseous  form. 

Mrs.  B.  Precisely  so.  But  I  should  not  forget  to  observe, 
that  the  wires  used  in  this  experiment  are  made  of  platina,  a 
metal  which  is  not  capable  of  combining  with  oxygen  ;  for 
otherwise  the  wire  would  combine  with  the  oxygen,  and  the  hy- 
drogen alone  would  be  disengaged. 

Caroline.  But  could  not  water  be  decomposed  without  the 
electric  circle  being  completed  ?  If,  for  instance,  you  immersed 
only  the  positive  wire  in  the  water,  would  it  not  combine  with 
the  oxygen,  and  the  hydrogen  gas  be  given  out  ? 

Mrs.  B.  No  ;  for  as  you  may  recollect,  the  battery  cannot 
act  unless  the  circle  be  completed;  since  the  positive  wire  will 
not  give  out  its  electricity,  unless  attracted  by  that  of  the  nega- 
tive wire. 

Caroline.  I  understand  it  now. — Bat  look,  Mrs.  B  ,  the  de- 
composition of  the  water  which  has  now  been  going  on  for  some 
time,  does  not  sensibly  diminish  its  quantity — what  is  the  rea- 
son of  that  ? 

Mrs.  B.  Because  the  quantity  decomposed  is  so  extremely 
small.  If  you  compare  the  density  of  water  with  that  of 
the  gases  into  which  it  is  resolved,  you  must  be  aware  that  a  sin- 
gle drop  of  water  is  sufficient  to  produce  thousands  of  such  small 
bubbles  as  those  you  now  perceive. 

Caroline.  But  in  this  experiment,  we  obtain  the  oxygen  and 
hydrogen  gases  mixed  together.  Is  there  any  means  of  procu- 
ring the  two  gases  separately  ? 

Mrs.  B.  They  can  be  collected  separately  with  great  ease, 
by  modifying  a  little  the  experiment.  Thus  if  instead  of  one 
tube,  we  employ  two,  as  you  see  here(c,  d,  PLATE  VIII.  fig.  2,) 
both  tubes  being  closed  at  one  end,  and  open  at  the  other ;  and 
if  after  filling  these  tubes  with  water,  we  place  them  standing  in 
a  glass  of  water  (e),  with  their  open  end  downwards,  you  will 
see  that  the  moment  we  connect  the  wires,  (a,  b)  which  proceed 
upwards  from  the  interior  of  each  tube,  the  one  with  one  end 
of  the  battery,  and  the  other  with  the  other  end,  the  water  in  the 
tubes  will  be  decomposed  ;  hydrogen  will  be  given  out  round 
the  wire  in  the  tube  connected  with  the  positive  end  of  the  bat- 
tery, and  oxygen  in  the  other ;  and  these  gases  will  be  evolved 
exactly  in  the  proportions  which  I  have  before  mentioned,  name- 


HYDROGfiNV  103 

ly,  two  measures  of  hydrogen  for  one  of  oxygen.  We  shall  now 
begin  the  experiment,  but  it  will  be  some  time  before  any  sensi- 
ble quantity  of  the  gases  can  be  collected. 

Emily.  The  decomposition  of  water  in  this  way,  slow  as  it  is, 
is  certainly  very  wonderful ;  but  I  confess  that  I  should  be  still 
more  gratified,  if  you  could  show  it  us  on  a  larger  scale,  and  by 
a  quicker  process.  I  am  sorry  that  the  decomposition  of  water 
by  charcoal  or  metals  is  attended  with  so  much  inconvenience. 

Mrs.  B.  Water  may  be  decomposed   by  means  of  metals 
without  any  difficulty  :  but  for  this  purpose  the  intervention  of 
an  acid  is  required.     Thus,   if  we  add  some  sulphuric  acid  (a 
substance  with  the  nature  of  whieh  you  are  not  yet  acquainted) 
to  the  water  which  the  metal  is  to  decompose,  the  acid  disposes 
the  metal  to  combine  with  the  oxygen  of  the  water  so  readily 
and  abundantly,  that  no  heat  is  required  to  hasten  the  process. 
Of  this  I  am  going  to  show  you  an  instance.     I  put  into  this  bot- 
tle the  water  that  is  to  be  decomposed,  as  also  the  metal  that  is. 
to  effect  that  decomposition   by   combining  with    the  oxygen, 
and  the  acid  which  is  to  facilitate  the  combination  of  the  metal 
and  the  oxygen.     You  will  see  with  what  violence  these  will  act 
on  each  other.* 

Caroline.  But  what  metal  is  it  that  you  employ  for  this  pur- 
pose? 

Mrs.  B.  It  is  iron ;  and  it  is  used  in  the  state  of  filings,  as 
these  present  a  greater  surface  to  the  acid  than  a  solid  piece  of 
metal.  For  as  it  is  the  surface  of  the  metal  which  is  acted  up- 
on by  the  acid,  and  is  disposed  to  receive  the  oxygen  produced 
by  the  decomposition  of  the  water,  it  necessarily  follows  that 
the  greater  is  the  surface,  the  more  considerable  is  the  effect. 
The  bubbles  which  are  now  rising  are  hydrogen  gas  — — 

Caroline.  How  disagreeably  it  smells  !  [Pure  hydrogen  is 
inodorous.  Q.J 

Mrs.  fi.  It  is  indeed  unpleasant,  though,  I  believe,  not  par- 

*  To  obtain  hydrogen,  fit  a  corK.  air  tight  to  an  oil  flask,  and  pierce 
it  with  a  burning  iron,  to  admit  a  tube.  The  tube  may  be  of  glass, 
lead,  or  tin,  bent  to  a  convenient  shape,  and  put  into  the  opening  made 
by  the  hot  iron.  Pour  into  the  flask  about  a  gill  of  water,  and  drop  in- 
to it  about  an  ounce  of  zinc,  granulated  by  melting,  and  pouring  it  in- 
to cold  water.  Then  pour  in  half  an  ounce  by  measure  of  sulphuric 
acid,  and  immediately  put  the  cork  into  its  place,  and  plunge  the  oth- 
er end  of  the  tube  under  a  receiver,  or  large  tumbler,  filled  with  water, 
and  inverted  in  the  water-bath.  The  flask  grows  hot  and  the  gas  be- 
gins to  rise,  the  instant  the  acid  is  poured  in  ;  a  place  therefore  must 
previously  be  prepared  to  set  it ;  and  if  nothing  better  is  at  hand,  a 
bowl,  with  a  cloth  in  it,  to  prevent  breaking  the  flask,  and  set  at  a 
convenient  height  will  do  very  well.  C, 


104  HYDROGEN, 

4 

ticularly  hurtful.  We  shall  not,  however,  suffer  any  more  to 
escape,  as  it  will  be  wanted  for  experiments.  1  shall,' therefore, 
collect  it  in  a  glass-receiver,  by  making  it  pass  through  this  bent 
tube,  which  will  conduct  it  into  the  water-bath.  (PLATE  VIII. 
fig.  3.) 

Emily.  How  very  rapidly  the  gas  escapes  !  it  is  perfectly 
transparent,  and  without  any  colour  whatever. — Now  the  re- 
ceiver is  full  — 

Mrs.  B.  We  shall,  therefore,  remove  it,  and  substitute  anoth- 
er in  its  place.  But  you  must  observe,  that  when  the  receiver 
is  full,  it  is  necessary  to  keep  it  inverted  with  the  mouth  under 
water,  otherwise  the  gas  would  escape.  And  in  order  that  it 
may  not  be  in  the  way,  I  introduce  within  the  bath,  under  the 
water,  a  saucer,  into  which  I  slide  the  receiver,  so  that  it  can 
be  taken  out  of  the  bath  and  conveyed  any  where,  the  water  in 
the  saucer  being  equally  effectual  in  preventing  its  escape  as 
that  in  the  bath.  (PLA/TE  VIII.  fig.  4.) 

Emily.  I  am  quite  surprised  to  see  what  a  large  quantity  of 
hydrogen  gas  can  be  produced  by  such  a  small  quantity  af  wa- 
ter, especially  as  oxygen  is  the  principal  constituent  of  water. 

Mrs.  B.  In  weight  it  is  ;  but  not  in  volume.  For  though  the 
proportion,  by  weight,  is  nearly  six  parts  of  oxygen  to  one  of 
hydrogen,  yet  the  proportion  of  the  volume  of  the  gases,  is 
about  one  part  of  oxygen  to  two  of  hydrogen  ;  so  much  heavier 
is  the  former  than  the  latter.* 

Caroline.  But  why  is  the  vessel  in  which  the  water  is  decom- 
posed so  hot  ?  As  the  water  changes  from  a  liquid  to  a  gaseous 
ibrm,  cold  should  be  produced  instead  of  heat. 

Mrs.  B.  No  ;  for  if  one  of  the  constituents  of  water  is  con- 
verted into  a  gas,  the  other  becomes  solid  in  combining  with  the 
metal. 

Emily.  In  this  case,  then,  neither  heat  nor  cold  should  be 
produced  ? 

Mrs.  B.  True ;  but  observe  that  the  sensible  heat  which  is 
disengaged  in  this  operation,  is  not  owing  to  the  decomposition 
of  the  water,  but  to  an  extrication  of  heat  produced  by  the  mix- 
ture of  water  and  sulphuric  acid.  I  will  mix  some  water  and 
sulphuric  acid  together  in  this  glass,  that  you  may  feel  the  sur- 
prising quantity  of  heat  which  is  disengaged  by  their  union — 
now  take  hold  of  the  glass 

Caroline.  Indeed  I  cannot ;  it  feels  as  hot  as  boiling  water. 
I  should  have  imagined  there  would  have  been  heat  enough  dis- 
engaged to  have  rendered  the  liquid  solid. 

*  Hydrogen  is  about  thirteen  times  lighter  than  atmospheric  air.  C 


HYDROGEN.  105 

Mrs.  B.  As,  however,  it  does  not  produce  that  effect,  we 
cannot  refer  this  heat  to  the  modification  called  latent  heat. 
We  may,  however,  I  think,  consider  it  as  heat  of  capacity,  since 
the  liquid  is  condensed  by  its  loss;  and  if  you  were  to  repeat 
the  experiment,  in  a  graduated  tube,  you  would  find  that  the 
two  liquids,  when  mixed,  occupy  considerably  less  space  than 
they  did  separately. — But  we  will  reserve  this  to  another  op- 
portunity, and  attend  at  present  to  the  hydrogen  gas  which  we 
have  been  producing. 

If  I  now  se,t  the  hydrogen  gas,  which  is  contained  in  this  re- 
ceiver, at  liberty  all  at  once,  and  kindle  it  as  soon  as  it  comes 
in  contact  with  the  atmosphere,  by  presenting  it  to  a  candle,  it 
will  so  suddenly  and  rapidly  decompose  the  oxygen  gas,  by 
combining  with  its  basis,  that  an  explosion,  or  a  detonation  (as 
chemists  commonly  call  it,)  will  be  produced.  For  this  pur- 
pose, I  need  only  take  up  the  receiver,  and  quickly  present  its 
open  mouth  to  the  candle so  ....... 

Caroline.  It  produced  only  a  sort  of  hissing  noise,  with  a 
vivid  flash  of  light.  I  had  expected  a  much  greater  report. 

Mrs.  B.  And  so  it  would  have  been,  had  the  gases  been 
closely  confined  at  the  moment  they  were  made  to  explode.  If,' 
for  instance,  we  were  to  put  in  this  bottle  a  mixture  of  hydro- 
gen gas  and  atmospheric  air  5  and  if,  after  corking  the  boillC, 
we  should  kindle  the  mixture  by  a  very  small  orifice,  from  the 
sudden  dilatation  of  the  gases  at  the  moment  of  their  combina- 
tion, the  bottle  must  either  fly  to  pieces,  or  the  cork  be  blown 
out  with  considerable  violence. 

Caroline.  But  in  the  experiment  which  we  have  just  seen,  if 
you  did  not  kindle  the  hydrogen  gas,  would  it  not  equally  com- 
bine with  the  oxygen  ? 

Mrs.  B.  Certainly  not  ;  for,  as  I  have  just  explained  to  you, 
it  is  necessary  that  the  oxygen  and  hydrogen  gases  be  burnt  to- 
gether, in  order  to  combine  chemically  and  produce  water. 

Caroline.  That  is  true;  but  I  thought  this  was  a  different 
combination,  for  I  see  no  water  produced. 

Mrs.  B.  The  water  resulting  from  this  detonation  was  so 
small  in  quantity,  and  in  such  a  state  of  minute  division,  as  to 
be  invisible.  But  water  certainly  was  produced  5  for  oxygen 
is  incapable  of  combining  with  hydrogen  in  any  other  propor- 
tions than  those  which  form  water ;  therefore  water  m  ust  al- 
ways be  the  result  of  their  combination. 

If,  instead  of  bringing  the  hydrogen  gas  into  sudden  contact 
with  the  atmosphere  (as  we  did  just  now)  so  as  to  make  the 
whole  of  it  explode  the  moment  it  is  kindled,  we  allow  but  a 
very  small  surface  of  gas  to  burn  in  contact  with  the  atmosphere, 


106  t  HYDROGEN. 

the  combustion  goes  on  quietly  and  gradually  at  the  point  of  CG& 
tact,  without  any  detonation,  because  the  surfaces  brought  to- 
gether are  too  small  for  the  immediate  union  of  gases.  The 
experiment  is  a  very  easy  one.  This  phial,  with  a  narrow 
neck,  (PLATE  VIII.  fig  5.)  is  full  of  hydrogen  gas,  and  is  care- 
fully corked.  If  I  take  out  the  cork  without  moving  the  phial  > 
and  quickly  approach  the  candle  to  the  orifice,  you  will  see  how 
different  the  result  will  be* 

Emily.  How  prettily  it  burns,  with  a  blue  flame !  The  flame 
is  gradually  sinking  within  the  phial — now  it  has  entirely  disap- 
peared. But  does  not  this  combustion  likewise  produce  water? 

Mi's.  B.  Undoubtedly.  In  order  to  make  the  formation  of 
the  water  sensible  to  you,  I  shall  procure  a  fresh  supply  of.  hy- 
drogen gas,  by  putting  into  this  bottle  (PLATE  VIII.  fig.  6.) 
iron-filings,  water,  and  sulphuric  acid,  materials  similar  to  those 
which  we  have  just  used  for  the  same  purpose.  I  shall  then 
cork  up  the  bottle,  leaving  only  a  small  orifice  in  the  cork,  with 
a  piece  of  glass-tube  fixed  to  it,  through  which  the  gas  will  issue 
in  a  continued  rapid  stream. 

Caroline.  I  hear  already  the  hissing  of  the  gas  through  the 
tube,  and  I  can  feel  a  strong  current  against  my  hand. 

Mrs,  B.  This  current  lam  going  to  kindle  with  the  candle 
—see  how  vividly  it  burns 

Emily.  It  burns  like  a  candle  with  a  long  flame.  But  why 
does  this  combustion  last  so  much  longer  than  in  the  former  ex- 
periment ? 

Mrs.  B.  The  combustion  goes  on  interruptedly  as  long  as  the 
new  gas  continues  to  be  produced.  Now  if  I  invert  this  recei- 
ver over  the  flame,  you  will  soon  perceive  its  internal  surface 
covered  with  a  very  fine  dew,  which  is  pure  water 1 

Caroline.  Yes,  indeed  ;  the  glass  is  now  quite  dim  with  mois- 
ture !  How  glad  1  am  that  we  can  sec  the  water  produced  by 
this  combustion. 

Emily.  It  is  exactly  what  I  was  anxious  to  see;  for  I  confess 
I  was  a  little  incredulous. 

Mrs.  B.  If  I  had  not  held  the  glass-bell  over  the  flame,  the 
water  would  have  escaped  in  the  state  of  vapour,  as  it  did  in  the 

*  T"he  levity  of  hydrogen  is  such,  that  if  a  vessel  he  filled  with  it, 
and  kept  inverted,  it  may  be  carried  ;<bout  the  room,  without  its  es- 
caping. The  above  experiment  therefore  may  be  nu.de  by  bringing 
a  small  jar,  or  tumbler  of  the  gas  over  a  lighted  lamp.  C. 

t  The  burning  of  a  candle,  lamp,  wood  &c.  always  produces  water. 
The  tallow  and  oil  cuntain  hydrogen,  and  during  combustion,  it  unites 
with  the  oxygen  of  the  atniosphere.  Hold  a  wide  tul-e  over  a  lamp, 
and  it  is  soon  covered  v;ith  moisture.  Wood  contains  hydrogen.  C 


HYDROGEN,  107 

[periment.  We  have,  here,  of  course,  obtained  but  a 
very  small  quantity  of  water;  but  the  difficulty  of  producing  a 
proper  apparatus,  with  sufficient  quantities  of  gases,  prevents 
my  showing  it  you  on  a  larger  scale. 

The  composition  of  water  was  discovered  about  the  same  pe- 
riod, both  by  Mr  Cavendish,  in  this  country,  and  by  the  cele- 
brated French  chemist,  Lavoisier.  The  latter  invented  a  very 
perfect  and  ingenious  apparatus  to  perform,  with  great  accura- 
cy, and  upon  a  large  scale,  the  formation  of  water  by  the  com- 
bination of  oxygen  and  hydrogen  gases.  Two  tubes,  convey- 
ing due  proportions,  the  one  of  oxygen,  the  other  of  hydrogen 
gas,  are  inserted  at  opposite  sides  of  a  large  globe  of  glass,  pre- 
viously exhausted  of  air;  the  two  streams  of  gas  are  kindled 
within  the  globe,  by  the  electrical  spark,  at  the  point  where 
they  come  in  contact ;  they  burn  together,  that  is  to  say,  the  hy- 
drogen combines  with  the  oxygen,  the  caloric  is  set  at  liberty, 
and  a  quantity  of  water  is  produced  exactly  equal,  in  weight,  to 
that  of  the  two  gases  introduced  into  the  globe. 

Caroline.  And  what  was  the  greatest  quantity  of  water  ever 
formed  in  this  apparatus  ? 

Mrs.  B.  Several  ounces ;  indeed,  very  nearly  a  pound,  if  I 
recollect  right ;  but  the  operation  lasted  many  days. 

Emily.  This  experiment  must  have  convinced  all  the  world 
of  the  truth  of  the  discovery.  Pray,  if  improper  proportions 
of  the  gases  were  mixed  and  set  fire  to,  what  would  be  the  re- 
sult ? 

Mrs.  B.  Water  would  equally  be  formed,  but  there  would  be 
a  residue  of  either  one  or  other  of  the  gases,  because,  as  I  have 
already  told  you,  hydrogen  and  oxygen  will  combine  only  in 
the  proportions  requisite  for  the  formation  of  water. 

Emily.  Look,  Mrs.  B.,  our  experiment  with  the  Voltaic  bat- 
tery (PLATE  VIII.  fig.  2.)  has  made  great  progress;  a  quanti- 
ty of  gas  has  been  formed  in  each  tube,  but  in  one  of  them  there 
is  twice  as  much  as  in  the  other. 

Mrs.  B.  Yes ;  because,  as  I  said  before,  water  is  composed 
of  two  volumes  of  hydrogen  to  one  of  oxygen — and  if  we  should 
now  mix  these  gases  together  and  set  fire  to  them  by  an  electric- 
al spark,  both  gases  would  entirely  disappear,  and  a  small  quan- 
tity of  water  would  be  formed. 

There  is  another  curious  effect  produced  by  the  combustion 
of  hydrogen  gas,  which  I  shall  show  you,  though  I  must  ac- 
quaint you  first,  that  I  cannot  well  explain  the  cause  of  it.  For 
this  purpose,  I  must  put  some  materials  into  our  apparatus,  in 
order  to  obtain  a  stream  of  hydrogen  gas,  just  as  we  have  done 
before.  The  process  is  already  going  or»;  and  the  gas  is  rush- 
ing through  the  tube — I  shall  now  kindle  it  with  the  taper 


108  HYDROGEN. 

Emily*  It  burns  exactly  as  it  did  before What  is  the  cu- 
rious effect  which  you  were  mentioning? 

Mrs.  B.  Instead  of  the  receiver,  by  means  of  which  we  have 
just  seen  the  drops  of  water  form,  we  shall  invert  over  the  flame 
this  piece  of  tube,  which  is  about  two  feet  in  length,  and  one 
inch  in  diameter  (PLATE  VIII.  fig.  7.;)  but  you  must  observe 
that  it  is  open  at  both  ends. 

Emily.  What  a  strange  noise  it  makes  !  something  like  the 
jEolian  harp,  but  not  so  sweet. 

Caroline.  It  is  very  singular,  indeed  ;  but  I  think  rather  too 
powerful  to  be  pleasing.  And  is  not  this  sound  accounted  for  ? 

Mrs.  B.  That  the  percussion  of  glass,  by  a  rapid  stream  of 
gas,  should  produce  a  sound,  is  not  extraoidinary  :  but  the 
sound  here  is  so  peculiar,  that  no  other  gas  has  a  similar  effect. 
Perhaps  it  is  owing  to  a  brisk  vibratory  motion  of  the  glass,  oc- 
casioned by  the  successive  formation  and  condensation  of  small 
drops  of  water  on  the  sides  of  the  glass  tube,  and  the  air  rush- 
ing in  to  replace  the  vacuum  formed.* 

Caroline.  How  very  much  this  flame  resembles  the  burning 
of  a  candle. 

Mrs.  B.  The  burning  of  a  candle  is  produced  by  much  the 
same  means.  A  great  deal  of  hydrogen  is  contained  in  candles, 
whether  of  tallow  or  wax.  This  hydrogen  being  converted  in- 
to gas  by  the  heat  of  the  candle,  combines  with  the  oxygen  of 
the  atmosphere,  and  flame  and  water  result  from  this  combina- 
tion.t  So  that,  in  fact,  the  flame  of  a  candle  is  owing  to  the 
combustion  of  hydrogen  gas.  An  elevation  of  temperature, 
such  as  is  produced  by  a  lighted  match  or  taper,  is  required  to 
give  the  first  impulse  to  the  combustion  ;  but  afterwards  it  goes 
on  of  itself,  because  the  candle  finds  a  supply  of  caloric  in  the 
successive  quantities  of  heat  which  results  from  the  union  of 
the  two  electricities  given  out  by  the  gases  during  their  combus- 
tion. But  there  are  other  circumstances  connected  with  the 
combustion  of  candles  and  lamps,  which  I  cannot  explain  to 
you  till  you  are  acquainted  with  carbon,  which  is  one  of  their 
constituent  parts.  In  general,  however,  whenever  you  see 
flame,  you  may  infer  that  it  is  owing  to  the  formation  and  burn- 
ing of  hydrogen  gas  :J  for  flame  is  the  peculiar  mode  of  burn- 

*  This  ingenious  explanation  was  first  suggested  by  Dr.  Delarive. — 
See  Journals  of  the  Royal  Institution,  vol.  i.  p  259. 

t  The  candle  also  contains  carbon,  which  gives  brilliancy  to  the 
flame,  and  the  product  of  the  combination  besides  flame  and  water  is  a 
quantity  of  carbonic  acid.  »  . 

$  Or  rather  hydro- carhonat,  a  gas  composed  of  hydrogen,  and  carbon, 
which  will  be  noticed  under  the  head  Carbon. 


HYDROGEN.  109' 

ing  hydrogen  gas,  which,  with  only  one  or  two  apparent  excep- 
tions, does  not  belong  to  any  other  combustible. 

Emily.  You  astonish  me  !  1  understood  that  flame  was  the 
caloric  produced  by  the  union  of  the  two  electricities,  in  all 
combustions  whatever  ? 

Mrs.  H.  Your  error  proceeded  from  your  vague  and  incor- 
rect idea  of  flame;  you  have  confounded  it  with  light  and  calo- 
ric in  general.  Flame  always  implies  caloric,  since  it  is  produ- 
ced by  the  combustion  of  hydrogen  gas  ;  but  all  caloric  does 
not  imply  flame.  Many  bodies  burn  with  intense  heat  without 
producing  flame.  Coals,  for  instance,  burn  with  flame  until 
all  the  hydrogen  which  they  contain  is  evaporated  ;  but  when 
they  afterwards  become  red  hot,  much  more  caloric  is  disengaged 
than  when  they  produce  flame. 

Caroline.  But  the  iron  wire,  which  you  burnt  in  oxygen  cas, 
appeared  to  me  to  emit  flame;  yet,  as  it  was  a  simple  metal,  it 
could  contain  no  hydrogen  ? 

Mrs.  B.  It  produced  a  sparkling  dazzling  blaze  of  light,  but 
no  real  flame. 

Caroline.  And  what  is  the  cause  of  the  regular  shape  of  the 
flame  of  a  candle  ? 

Mrs.  B.  The  regular  stream  of  hydrogen  gas  which  exhales 
from  its  combustible  matter. 

Caroline.  But  the  hydrogen  gas  must,  from  its  great  levity, 
ascend  into  the  upper  regions  of  the  atmosphere  :  why  there- 
fore does  not  the  flame  continue  to  accompany  it  ? 

Mrs,  B.  The  combustion  of  the  hydrogen  gas  is  completed 
at  the  point  where  the  flame  terminates;  it  then  ceases  to  be 
hydrogen  gas,  as  it  is  converted  by  its  combination  with  oxygen 
into  watery  vapour;  but  in  a  state  of  such  minute  division  as  to 
be  invisible. 

Caroline.  I  do  not  understand  what  is  the  use  of  the  wick  of 
a  candle,  since  the  hydrogen  gas  burns  so  well  without  it  ? 

Mrs.  B.  The  combust  ble  matter  of  the  candle  must  be  de- 
composed in  order  to  emit  the  hydrogen  gas,  and  the  wick  is 
instrumental  in  effecting  this  decomposition.  Its  combustion 

first  melts  the  combustible  matter,  and 

Caroline.  But  in  lamps  the  combustible  matter  is  already 
fluid,  and  yet  they  also  require  wicks  ? 

Mrs.  B.  I  am  going  to  add  that,  afterwards,  the  burning  wick 

(by  the  power  of  capillary  attraction)  gradually  draws  up  the 

fluid  to  the  point  where  combustion  takes  place;    for  you  must 

have  observed  that  the  wick  does  not  burn  quite  to  the  bottoms 

Caroline.  Yes ;  but  I  do  not  understand  why  it  does  not. 

Mrs.  B.  Because  the  air  has  not  so  free  an  access  to  that 

11 


110  HYDROGEN. 

part  of  the  wick  which  is  immediately  in  contact  with  the  can- 
dle, as  to  the  part  just  above,  so  that  the  heat  there  is  not  suffi- 
cient to  produce  its  decomposition;  the  combustion  therefore 
begins  a  little  above  this  point.* 

Caroline.  But,  Mrs.  B.  in  those  beautiful  lights,  called  gas- 
ligids.,  which  are  now  seen  in  many  streets,  and  will,  I  hope,  be 
soon  adopted  every  where,  I  can  perceive  no  wick  at  all.  How 
are  these  lights  managed  ? 

Mrs.  B.  I  am  glad  you  have  put  me  in  mind  of  saying  a  few 
words  on  this  very  useful  and  interesting  improvement.  In  this 
mode  of  lighting,  the  gas  is  conveyed  to  the  extremity  of  a 
tube,  where  it  is  kindled,  and  burns  as  long  as  the  supply  con- 
tinues. There  is,  therefore,  no  occasion  for  a  wick,  or  any 
other  fuel  whatever. 

Emily.  But  how  is  this  gas  procured  in  such  large  quanti- 
ties ? 

Mrs.  B.  It  is  obtained  from  c0al,  by  distillation. — Coal, 
when  exposed  to  heat  in  a  close  vessel,  is  decomposed  ;  and  hy- 
drogen, which  is  one  of  its  constituents,  rises  in  the  state  of  gas, 
combined  with  another  of  its  component  parts,  carbon,  forming 
a  compound  gas,  called  IJydro-carbonat,  the  nature  of  which 
we  shall  again  have  an  opportunity  of  noticing  when  we  treat 
of  carbon.  This  gas,  like  hydrogen,  is  perfectly  transparent,  in- 
visible, and  highly  inflammable;  and  in  burning  it  emits  that 
vivid  light  which  you  have  so  often  observed. 

Caroline.  And  does  the  process  for  procuring  it  require  no- 
thing but  heating  the  coals,  and  conveying  the  gas  through 
tubes  ? 

Mrs.  B.  Nothing  else  ;  except  that  the  gas  must  be  made  to 
pass,  immediately  at  its  formation,  through  two  or  three  large- 
vessels  of  water,!  in  which  it  deposits  some  other  ingredients, 
and  especially  water,  tar,  and  oil,  which  also  arise  from  tin 
distillation  of  coals.  The  gas-light  apparatus,  therefore  con- 
sists simply  in  a  large  iron  vessel,  in  which  the  coals  are  expo- 
sed to  the  heat  of  a  furnace, — some  reservoirs  of  water,  in 

*  Tn  the  burning  of  a  candle,  the  reason  why  ccmhustion  does  not 
take  place  in  immediate  contact  with  the  tallow  is,  that  the  caloric 
is  here  employed  in  converting;  a  solid  into  a  fluid,  as  explained  in 
the  conversation  of  free  caloric.  In  the  burning  01  a  lamp  if  the 
same  thing  takes  place,  it  is  because  the  metallic  tube  through  which 
.the  wick  passes,  conducts  off  the  heat.  C. 

t  The  gas  is  passed  through  one  vessel  of  slacked  lime  and  water  to 
absorb  the  carbonic  acid  gas,  with  which  it  is  always  more  or  less  mix 
ed,  whea  first  distilled.     C. 


HYDROGEN.  Ill 

which  the  gas  deposits -its  impurities, — and  tubes  that  convey 
it  to  the  desired  spot,  being  propelled  with  uniform  velocity 
through  the  tubes  by  means  of  a  certain  degree  of  pressure 
which  is  made  upon  the  reservoir. 

Emily.  What  an  admirable  contrivance  !  Do  you  not  think, 
Mrs.  B.,  that  it  will  soon  get  into  universal  use  ? 

Airs.  B.  Most  probably,  for  the  purpose  of  lighting  streets, 
offices,  and  public  places,  as  it  far  surpasses  any  former  inven- 
tion for  that  purpose;  but  in  regard  to  the  interior  of  private 
houses,  this  mode  of  lighting  has  not  yet  been  sufficiently  tried 
to  know  whether  it  will  be  found  generally  desirable,  either  with 
respect  to  economy  or  convenience.  It  may,  however,  be  con- 
sidered as  one  of  the  happiest  applications  of  chemistry  to  the 
comforts  of  life;  and  there  is  every  reason  to  suppose  that  it 
will  answer  the  full  extent  of  public  expectation. 

I  have  another  experiment  to  show  you  with  hydrogen  gas, 
which  I  think  will  entertain  you.  Have  you  ever  blown  bub- 
bles with  soap  and  water  ? 

Emily.  Yes,  often,  when  I  was  a  child  ;  and  I  used  to  make 
them  float  in  the  air  by  blowing  them  upwards. 

Mrs.  B.  We  shall  fill  some  such  bubbles  with  hydrogen  gas, 
instead  of  atmospheric  air,  and  you  will  see  with  what  ease  and 
rapidity  they  will  ascend,  without  the  assistance  of  blowing, 
from  the  lightness  of  the  gas. — Will  you  mix  some  soap  and 
water  whilst  I  fill  this  bladder  with  the  gas  contained  in  the  re- 
ceiver which  stands  on  the  shelf  in  the  water-bath  ? 

Caroline.  What  is  the  use  of  the  brass-stopper  and  turn-cock 
at  the  top  of  the  receiver  ? 

Mrs.  B.  It  is  to  afford  a  passage  to  the  gas  when  required. 
There  is,  you  see,  a  similar  stop-cock  fastened  to  this  bladder, 
which  is  made  to  fit  that  on  the  receiver.  I  screw  them  one  on 
the  other,  and  now  turn  the  two  cocks,  to  open  a  communica- 
tion between  the  receiver  and  the  bladder;  then,  by  sliding  the 
receiver  oft* the  shelf,  and  gently  sinking  it  into  the  bath,  the 
water  rises  in  the  receiver  and  forces  the  gas  into  the  bladder. 
(PLATE  IX.  fig.  1.) 

Caroline.  Yes,  I  see  the  bladder  swell  as  the  water  rises  in 
the  receiver. 

Mrs.  B.  I  think  that  we  have  already  a  sufficient  quantity  in 
the  bladder  for  our  purpose ;  we  riuist  be  careful  to  stop  both 
ihe  cocks  before  we  separate  the  bladder  from  the  receiver,  lest 
the  gas  should  escape. — Now  I  must  fix  a  pipe  to  the  stopper 
of  the  bladder,  and  by  dipping  its  mouth  into  the  soap  and  wa- 
ter, take  up  a  few  drops — then  I  again  turn  the  cock,  and 


112 


HYDROGEN. 


squeeze  the  bladder  in  order  to  force  the  ?as  into  the  soap  aim 
water  at  the  mouth  of  the  pipe.  (PLATE  !  X.  fig.  2.) 

Emily.  There  is  a  bubble — but  it  bursts  before  it  leaves  the 
mout;i  ot'ihe  i>ipe. 

Mrs.  IL  We  must  have  patience  and  try  again  ;  it  is  not  so 
easy  to  blow  bubbles  by  means  of  a  •>!  idder.  as  simply  with  the 
breath. 

Caroline.  Perhaps  there  is  not  soap  enough  in  the  water  ;  I 
should  liave  na(]  Wann  water,  it  would  have  dissolved  the  soar) 
b  ter. 

Emily.  Does  not  some  of  the  gas  escape  between  the  blad- 
der and  the  pipe? 

Mrs.  B.  No,  they  are  perfectly  air  tight;  we  shall  succeed 
presently,  I  dare  say. 

Caroline.  Now  a  bubble  ascends  ;  it  moves  with  the  rapidi- 
ty of  a  balloon.  How  beautifully  it  refracts  the  light  ! 

Emily.  It  has  burst  against  the  ceiling — you  succeed  now 
wonderfully ;  but  why  do  they  all  ascend  and  burst  against  the 
ceiling  ? 

Mrs.  B.  Hydrogen  gas  is  so  much  lighter  than  atmospherical 
air,  that  it  ascends  rapidly  with  its  very  light  envelope,  which  is 
burst  by  the  force  with  which  it  strikes  the  ceiling. 

Air-balloons  are  filled  with  this  gas,  and  if  they  carried  no 
other  weight  than  their  covering,  would  ascend  as  rapidly  as 
these  bubbles. 

Caroline.  Yet  their  covering  must  be  much  heavier  than  that 
of  these  bubbles  ? 

Mrs.  B.  Not  in  proportion  to  the  quantity  of  gas  they  con- 
tain. I  do  not  know  whether  you  have  ever  been  present  at 
the  filling  of  a  large  balloon.  The  apparatus  for  that  purpose 
is  very  simple.  It  consists  of  a  number  of  vessels,  either  jars  or 
barrels,  in  which  the  materials  for  the  formation  of  the  gas  are 
mixed,  each  of  these  being  furnished  with  a  tube,  and  communi- 
cating with  along  flexible  pipe,  which  conveys  the  gas  into  the 
balloon. 

Emily.  But  the  fire-balloons  which  were  first  invented,  and 
have  been  since  abandoned,  on  account  of  their  being  so  dan- 
gerous, were  constructed,  I  suppose,  on  a  different  principle. 

J\1rs.  /..'.  They  were  filled  simply  with  atmospherical  air, 
considerably  rarified  by  heat  5  and  the  necessity  of  having  a 
fire  underneath  the  balloon,  in  order  to  preserve  the  rarefaction 
of  the  air  within  it,  was  the  circumstance  productive  of  so  much 
tlanper. 

If  you  are  not  yet  tired  of  experiments,  I  have  another  to 
show  you.  It  consists  in  filling  soap-bubbles  with  a  mixture  of 


HYDROGEN*  J  1^ 

0 

hydrogen  and  oxygen  gases,  in  the  proportions  that  form  water; 
and  afterwards  setting  fire  to  them. 

Emily.  They  will  detonate,  1  suppose? 

J\Jrs.  i>.  Yes,  they  will.  As  you  have  seen  the  method  of 
transferring  the  gas  from  the  receiver  into  the  bladder,  it  is  not 
necessary  to  repeat  it.  I  have  therefore  provided  a  bladder 
which  contains  a  due  proportion  of  oxygen  and  hydrogen  gases, 
and  we  have  only  to  blow  bubbles  with  it. 

Caroline.  Here  is  a  fine  large  bubble  rising — shall  I  set  fire 
to  it  with  the  candle  ? 

Mrs.  B.  If  you  please. 

Caroline.  Heavens,  what  an  explosion!* — It  Was  like  the 
report  of  a  gun :  I  confess  it  frightened  me  much.  I  never 
should  have  imagined  it  could  be  so  loud. 

Emily.  And  the  flash  was  as  vivid  as  lightning. 

Mrs.  R.  The  combination  of  the  two  gases  takes  place  du- 
ring that  instant  of  time  that  you  see  the  flash,  and  hear  the  de- 
tonation. 

Emily.  This  has  a  strong  resemblance  to  thunder  and  light- 
ning.t 

Mrs.  R.  These  phenomena,  however,  are  generally  of  an 
electrical  nature.  Yet  various  meteorological  effects  may  be  at- 
tributed to  accidental  detonations  of  hydrogen  gas  in  the  atmos- 
phere; for  nature  abounds  with  hydrogen  :  it  constitutes  a  very 
considerable  portion  of  the  whole  mass  of  water  belonging  to 
our  globe,  and  from  that  source  almost  every  other  body  obtains 
it.  It  enters  into  the  composition  of  all  animal  substances, 
and  of  a  great  number  of  minerals;  but  it  is  most  abundant  in 
vegetables.  From  this  immense  variety  of  bo-lies,  it  is  often 
spontaneously  disengaged  ;  its  great  levity  makes  it  rise  into  the 
superior  regions  of  the  atmosphere ;  and  when,  either  by  an 
electrical  spark,  or  any  casual  elevation  of  temperature,  it  takes 
fire,  it  may  produce  such  meteors  or  luminous  appearances  as 
are  occasionally  seen  in  the  atmosphere.  Of  this  kind  are 
probably  those  broad  flashes  which  w**  often  see  on  a  summer- 
evening,  without  hearing  any  detonation. 

Emily.  Every  flash,  I  suppose,  must  produce  a  quantity  of 
water  ? 

*  In  making  this  experiment,  always  be  careful  to  turn  the  stop-cock, 
or  detach  the  bubble  completely  from  the  pipe  before  it  is  set  fire  to  ; 
otherwise  a  sad  accident  may  happen  from  the  gas  taking  fire  in  the 
bladder.  C. 

t  The  report  is  owing  to  the  air,  rushing  in  io  fill  the  vacuum,  cau- 
sed by  the  condensation  of  the  two  gasses  aad  the  heat  extricated  at 
Ihe  same  instant.  C, 

11* 


114  HYDROGEN. 

Caroline.  And  this  water,  naturally,  descends  in  the  form  of 
rain  ? 

Mrs.  B.  That  probably  is  often  the  case,  though  it  is  not  a 
necessary  consequence;  for  the  water  may  be  dissolved  by  the 
atmosphere,  as  it  descends  towards  the  lower  regions,  and  re- 
main there  in  the  form  of  clouds. 

The  application  of  electrical  attraction  to  chemical  phenom- 
ena is  likely  to  lead  to  many  very  interesting  discoveries  in  me- 
teorology ;  for  electricity  evidently  acts  a  most  important  part 
in  the  atmosphere.  This  subject  however  is,  as  yet,  not  suffi- 
ciently developed  for  me  to  venture  enlarging  upon  it.  The 
phenomena  of  the  atmosphere  are  far  from  being  well  under- 
stood ;  and  even  with  the  little  that  is  known,  I  arn  but  imper- 
fectly acquainted. 

But  before  we  take  leave  of  hydrogen,  I  must  not  omit  to 
mention  to  you  a  most  interesting  discovery  of  Sir  H.  Davy, 
which  is  connected  with  this  subject. 

Caroline.  You  allude,  I  suppose,  to  the  new  miner's  lamp, 
which  has  of  late  been  so  much  talked  of?  I  have  long  been 
desirous  of  knowing  what  that  discovery  was,  and  what  pur- 
pose it  was  intended  to  answer. 

Mrs.  B.  It  often  happens  in  coal-mines,  that  quantities  of  the 
gas,  called  by  chemists  kydro-carbonat,  or  by  the  miners  fire- 
damp, (ihe  same  from  which  the  gas-lights  are  obtained,)  ooze 
Out  from  fissures  in  the  beds  of  coal,  and  fill  the  cavities  in 
which  the  men  are  at  work ;  and  this  gas  being  inflammable, 
the  consequence  is,  that  when  the  men  approach  those  places 
with  a  lighted  candle,  the  gas  takes  fire,  and  explosions  happen 
which  destroy  the  men  and  horses  employed  in  that  part  of  the 
coll'ery,  sonriftimes  in  great  numbers. 

Emily-  What  tremendous  accidents  these  must  be  !  Bufc 
whence  does  that  gas  originate  ? 

Mrs.  B.  Being  the  chief  product  of  the  combustion  of  coal, 
no  wonder  that  inflammable  gas  should  occasionally  appear  in 
situations  in  which  this  mineral  abounds,  since  there  can  be  no 
doubr  that  processes  of  combustion  are  frequently  taking  place 
at  a  ereat  depth  under  the  surface  of  the  earth  ;  and  therefore 
thosf  accumulations  of  gas  may  arise  either  from  combustions 
actually  going  on,  or  from  former  combustions,  the  gas  having 
perhaps  been  confined  there  for  ages. 

Caroline.  And  how  does  Sir  H.  Davy's  lamp  prevent  those 
dreadful  explosions? 

Mrs.  B.  By  a  contrivance  equally  simple  and  ingenious ; 
and  one  which  does  no  less  credit  to  the  philosophical  views 
from  which  it  was  deduced,  than  to  the  philanthropic  motive? 


HYDROGEN.  11 3 

Irom  which  the  enquiry  sprung.  The  principle  cf  the  lamp  is 
shortly  this  :  It  was  ascertained,  two  or  three  years  ago,  both 
by  Mr.  Tenant  and  by  Sir  Humphrey  himself,  that  the  combus- 
tion of  inflammable  gas  could  not  be  propagated  through  small 
tubes  ;  so  that  if  a  jet  of  an  inflameable  gaseous  mixture,  issu- 
ing from  a  bladder  or  any  other  vessel,  through  a  small  tube, 
be  set  fire  to,  it  burns  at  the  orifice  of  the  tube,  but  the  flame 
never  penetrates  into  the  vessel.  It  is  upon  this  fact  that  Sir 
Humphrey's  safety  lamp  is  founded. 

Emily.  But  why  does  not  the  flame  ever  penetrate  through 
the  tube  into  the  vessel  from  which  the  gas  issues,  so  as  to  ex- 
plode at  once  the  whole  of  the  gas  ? 

Airs.  B.  Because,  no  doubt,  the  inflamed  gas  is  so  much  cool- 
ed in  its  passage  through  a  small  tube  as  to  cease  to  burn  be- 
fore the  combustion  reaches  the  reservoir. 

Caroline.  And  how  can  this  principle  be  applied  to  the  con- 
struction of  a  lamp  ! 

Mr*,  h.  Nothing  easier.  You  need  only  suppose  a  lamp 
enclosed  all  round  in  glass  or  horn,  hut  having  a  number  of 
small  open  tubes  at  the  bottom,  and  others  at  the  top,  to  let  the 
air  in  and  out.  Now,  if  such  a  lamp  or  lanthorn  be  carried  in- 
to an  atmosphere  capable  of  exploding,  an  explosion  or  com- 
bustion of  the  gas  will  take  place  within  the  lamp;  and  al- 
though the  vent  afforded  by  the  tubes  will  save  the  lamp  from 
bursting,  yet,  from  the  principle  just  explained,  the  combustion 
will  not  be  propagated  to  the  external  air  through  the  tubes,  so 
that  no  farther  consequence  will  ensue. 

Emily.  And  is  that  all  the  mystery  of  that  valuable  lamp? 

Mrs.  B.  No;  in  the  early  part  of  the  enquiry  a  lamp  of  this 
kind  was  actually  proposed  ;  but  it  was  but  a  rude  sketch  com- 
pared to  its  present  state  of  improvement.  Sir  H.  Davy,  after 
.  a  succession  of  trials,  by  which  he  brought  his  lamp  nearer  and 
nearer  to  perfection,  at  lasi  conceived  the  happy  idea  that  if  the 
lamp  were  surrounded  with  a  wire-work  or  wire-gauze,  of  a 
close  texture,  instead  of  glass  or  horn,  the  tubular  contrivance  I 
have  just  described  would  be  entirely  superseded,  since  each  of 
the  interstices  of  the  gauze  would  act  as  a  tube  in  preventing  the 
propagation  of  explosions  ;  so  that  this  previous  metallic  cover- 
ing would  answer  the  various  purposes  of  transparency,  of  per- 
meability to  air,  and  of  protection  against  explosion.  This 
idea,  Sir  Humphrey  immediately  submitted  to  the  test  of  exp€r- 
iment,  and  the  result  has  answered  his  most  sanguine  expecta- 
tions, both  in  his  laboratory  and  in  the  collieries,  where  it  has 
already  been  extensively  tried.  And  he  has  now  the  happiness 
of  thinking  that  his  invention  will  probably  be  the  means  of  sa- 


116  SULPHUR, 

ving  every  year  a  number  of  lives,  which  would  have  been  lost 
in  digging  out  of  the  bowels  of  the  earth  one  of  the  most  \Hilua- 
ble  necessaries  of  life.  Here  is  one  of  these  lamps,  everv  part 
of  which  you  will  at  once  comprehend.  (See  PLATE  X.  fig.  1.) 

Caroline.  How  very  simple  and  ingenious  !  But  I  do  not 
yet  well  see  why  an  explosion  taking  place  within  the  lamp 
should  not  communicate  to  the  external  air 'around  it,  through 
the  interstices  of  the  wire? 

Mrs.  8.  This  has  been  and  is  still  a  subject  of  wonder,  even 
to  philosophers ;  and  the  only  mode  of  explaining  it  is,  that 
flame  or  ignition  cannot  pass  through  a  fine  wire-work,  because 
the  metallic  wire  cools  the  flame  sufficiently  to  extinguish  it  in 
passing  through  the  gauze.  This  property  of  the  wire-gauze  is 
quite  similar  to  that  of  the  tubes  which  I  mentioned  on  introdu- 
cing the  subject ;  for  you  may  consider  each  interstice  of  the 
gauze  as  an  extremely  short  tube  of  a  very  small  diameter. 

Emihj.  But  I  should  expect  the  wire  would  often  become 
red-hot,  by  the  burning  of  the  gas  within  the  lamp  ? 

Mrs.  B.  And  this  is  actually  the  case,  for  the  top  of  the 
lamp  is  very  apt  to  become  red-hot.  But,  fortunately,  inflam- 
mable gaseous  mixtures  cannot  be  exploded  by  red-hot  wire, 
the  intervention  of  actual  flame  being  required  forthat  purpose; 
so  that  the  wire  does  not  set  fire  to  the  explosive  gas  around  it. 

Emily.  I  can  understand  that;  but  if  the  wire  be  red-hot, 
how  can  it  cool  the  flame  within,  and  prevent  its  passing 
through  the  gauze  ? 

Mrs.  h.  The  gauze,  though  red-hot,  is  not  so  hot  as  the  flame 
by  which  it  has  been  heated  ;  and  as  metalic  wire  is  a  good  con- 
ductor, the  heat  does  not  much  accumulate  in  it,  as  it  passes  off 
quickly  to  the  other  parts  of  the  lamp,  as  well  as  to  any  contig- 
uous bodies. 

Caroline.  This  is  indeed  a  most  interesting  discovery,  and 
one  which  shows  at  once  the  immense  utility  with  which  science 
may  be  practically  applied  to  some  of  the  most  important  pur- 
poses. 


CONVERSATION  VIII. 

ON  SULPHUR  AND  PHOSPHORUS. 

^ 

Mrs.  B.  SULPHUR  is  the  next  substance  that  comes  under  oui 
consideration.     It  differs  in  one  essential  point  from  the  prr 


.A..  f7if  fiftfrn.     containing  tfu  ait  '._B.  1/u  rtin  or 
<ff*/ir/'.>  £y  u7itf&  /fit  ^atuze   capf  if  /KWO?  to  die  ns-tern  .—Q. 

t'rip  <?/7._E.#  Kin;  &r  tritmmry&e  wit&  D  __  T1//4"  wine  gauze  eyfaiJrr. 


(s. 


^/?__B.  t/tt 


K 


SCJLHHUR.  117 

Ceding,  as  it  exists  in  a  solid  form  at  the  temperature  of  the  at- 
mosphere. 

Caroline.  lam  glad  that  we  have  at  last  a  solid  body  to  ex- 
amine ;  one  that  we  can  see  and  touch.  Pray,  is  it  not  with 
sulphur  that  the  points  of  matches  are  covered,  to  make  them 
easily  kindle  ? 

Jftrs.  B.  Yes,  it  is  ;  and  you  therefore  already  know  that 
sulphur  is  a  very  combustible  substance.  It  is  seldom  discov- 
ered in  nature  in  a  pure  unmixrd  state;  so  great  is  its  affinity 
for  other  substances,  that  it  is  almost  constantly  found  combined 
with  some  of  them.  It  is  most  commonly  united  with  metals, 
under  various  forms,  and  is  separated  from  them  by  a  very  sim- 
ple process.  It  exists  likewise  in  many  mineral  waters,  and 
some  vegetables  yield  it  in  various  proportions,  especially  those 
of  the  cruciform  tribe.  It  is  also  found  in  animal  matter;  in 
short  it  may  be  discovered  in  greater  or  less  quantity,  in  the 
mineral,  vegetable,  and  animal  kingdoms.* 

Emily.  I  have  heard  oi'fowers  qf  sulphur,  are  they  the  pro- 
duce of  any  plant  ? 

Mrs.  B.  By  no  means  :  they  consist  of  nothing  more  than 
common  sulphur,  reduced  to  a  very  fine  powder  by  a  process 
called  sublimation. — You  see  some  of  it  in  this  phial ;  it  is  ex- 
actly the  same  substance  as  this  lump  of  sulphur,  only  its  colour 
is  a  paler  yellow,  owing  to  its  state  of  very  minute  division. 

Emily.  Pray  what  is  sublimation  ? 

Mrs.  B.  It  is  the  evaporation,  or,  more  properly  speaking, 
the  volatilisation  of  solid  substances,  which,  in  cooling,  con- 
dense again  in  a  concrete  form.  The  process,  in  this  instance, 
must  be  performed  in  a  closed  vessel,  both  to  prevent  combus- 
tion, which  would  take  place  if  the.  access  of  air  were  not  care- 
fully precluded,  and  likewise  in  order  to  collect  the  substance 
after  the  operation.  As  it  is  rather  a  slow  process,  we  shall 
not  try  the  experiment  now  ;  but  you  will  understand  it  per- 
fectly if  I  show  you  the  apparatus  used  for  the  purpose.  (PLATE 
XI.  fig.  1.)  Some  lumps  of  sulphur  are  put  into  a  receiver  of 
this  kind,  winch  is  called  a  cucurbit.  Its  shape,  you  see,  some- 
what resembles  that  of  a  pear,  and  is  open  at  the  top,  so  as  to 
adapt  itself  exactly  to  a  kind  of  conical  receiver  of  this  sort, 
called  the  head.  The  cucurbit,  thus  covered  with  its  head,  is 
placed  over  a  sand-bath  :  this  is  nothing  more  than  a  vessel 
lull  of  sand,  which  is  kept  heated  by  a  furnace,  such  as  you  see 

*  The  sulphur  of  commerce  is  chiefly  obtained  in  the  vicinity  of 
volcanoes,  or  in  volcanic  countries,  where  it  is  brought  up  from  the 
how  •]«  <>f  the  t-nrlh  by  sublimation.  An  inferior  kind  is  obtained  by 
(lie  distillation  of  pyrites.  C 


118  SULPHUR. 

here,  so  as  to  preserve  the  apparatus  in  a  moderate  and  unifonu 
temperature.  The  sulphur  then  soon  begins  to  melt,  and  im- 
mediately after  this,  a  thick  white  smoke  rises,  which  is  gradu- 
ally deposited  within  the  head,  or  upper  part  of  the  apparatus, 
where  it  condenses  against  the  sides,  somewhat  in  the  form  of  a 
vegetation,  whence  it  has  obtained  the  name  of  ilowers  of  sul- 
phur. This  apparatus,  which  is  called  an  alembic,  is  highly 
useful  in  all  kinds  of  distillations,  as  you  will  see  when  we  come 
to  treat  of  those  operations.  Alembics  are  not  commonly  made 
of  glass,  like  this,  which  is  applicable  only  to  distillations  upon 
a  very  small  scale.  Those  used  in  manufactures  are  generally 
made  of  copper,  and  are,  of  course,  considerably  larger.  The. 
general  construction,  however,  is  always  the  same,  although 
their  shape  admits  of  some  variation. 

Caroline.  What  is  the  use  of  that  neck,  or  tube,  which  bend? 
down  from  the  upper  piece  of  the  apparatus? 

Mrs.  B.  it  is  of  no  use  in  sublimations  ;  but  in  distillations 
(the  general  object  of  which  is  to  evaporate,  by  heat,  in  closed 
vessels,  the  volatile  parts  of  a  compound  body,  and  to  condense 
them  again  into  a  liquid,)  it  serves  to  carry  off  the  condensed 
fluid,  which  otherwise  would  fall  back  into  the  cucurbit.  But 
this  is  rather  foreign  to  our  present  subject.  Let  us  return  to 
the  sulphur.  You  now  perfectly  understand,  I  suppose,  what 
is  meant  by  sublimation  ? 

Emily.  I  believe  I  do.  Sublimation  appears  to  consist  in 
destroying,  by  means  of  heat,  the  attraction  of  aggregation  of 
the  particles  of  a  solid  body,  which  are  thus  volatilised  ;  and  as 
soon  as  they  lose  the  caloric  which  produced  that  effect,  they 
are  deposited  in  the  fumi  of  a  fine  powder. 

Caroline.  It  seems  to  me  to  be  somewhat  similar  to  the  trans- 
formation of  water  into  vapour,  which  returns  to  its  liquid  state 
when  deprived  of  caloric. 

Emily.  There  is  this  difference,  however,  that  the  sulphur 
does  not  return  to  its  former  state,  since  instead  of  lumps,  it 
changes  to  a  fine  powder. 

Mrs.  B.  Chemically  speaking,  it  is  exactly  the  same  sub- 
stance, whether  in  the  form  of  lump  or  powder.  For  if  this 
powder  be  melted  again  by  heat,  it  will,  in  cooling,  be  restored 
to  the  same  solid  state  in  which  it  was  before  its  sublimation. 

Caroline.  But  if  there  be  no  real  change,  produced  by  the 
sublimation  of  the  sulphur,  what  is  the  use  of  that  operation? 

A!rs.  '}.  It  divides  the  sulphur  into  very  minute  parts,  and 
thus  disposes  it  to  enter  more  readily  into  combination  with 
other  bodies.  It  is  used  also  as  a  means  of  purification. 


SULPHUR.  Hi) 

Caroline.  Sublimation  .appears  to  me,  like  the  beginning  ot' 
combustion,  for  the  completion  of  which  one  circumstance  only 
is  wanting,  the  absorption  of  oxygen. 

Mrs.  B.  But  that  circumstance  is  every  thing.  No  essential 
alteration  is  produced  in  sulphur  by  sublimation  ;  whilst  in  com- 
bustion it  combines  with  the  oxygen,  and  forms  a  new  com- 
pound totally  different  in  every  respect  from  Sulphur  in  its  pure 
state. — We  shall  now  burn  some  sulphur,  and  you  will  see  how 
very  different  the  result  will  be.  For  this  purpose  I  put  a  small 
quantity  of  flowers  of  sulphur  into  this  cup,  and  place  it  in  a 
dish,  into  which  I  have  poured  a  little  water  :  I  now  set  fire  to 
the  sulphur  with  the  point  of  this  hot  wire  ;  for  its  combustion 
will  not  begin  unless  its  temperature  be  considerably  raised. — 
You  see  that  it  burns  with  a  faint  blueish  flame  :  and  as  I  invert 
over  it  this  receiver,  white  fumes  arise  from  the  sulphur,  and 
fill  the  vessel. — You  will  soon  perceive  that  the  water  is  rising 
within  the  receiver,  a  little  above  its  level  in  the  plate.  Well, 
Emily,  can  you  account  for  this  ? 

Emily.  I  suppose  that  the  sulphur  has  absorbed  the  oxygen 
from  the  atmospherical  air  within  the  receiver,  and  that  we  shall 
find  some  oxygenated  sulphur  in  the  cup.  As  for  the  white 
smoke,  I  arn  quite  at  a  loss  to  guess  what  it  may  be. 

Mrs.  B.  Your  first  conjecture  is  very  right ;  but  you  are 
mistaken  in  the  last  ;  for  nothing  will  be  left  in  the  cup.  The 
white  vapour  is  the  oxygenated  sulphur,  which  assumes  the  form 
of  an  elastic  fluid  of  a  pungent  and  offensive  smell,  and  is  a  pow- 
erful acid.  Here  you  see  a  chemical  combination  of  oxygen  and 
sulphur,  producing  a  true  gas,  which  would  continue  such  un- 
der the  pressure  and  at  the  temperature  of  the  atmosphere,  if  it 
did  not  unite  with  the  water  in  the  plate,  to  which  it  imparts  its 
acid  taste,  and  all  its  acid  properties.  You  see,  now,  with 
what  curious  effects  the  combustion  of  sulphur  is  attended: 

Caroline.  This  is  something  quite  new  ;  and  I  confess  that 
T  do  not  perfectly  understand  why  the  sulphur  turns  acid. 

Mrs.  B.  It  is  because  it  unites  with  oxygen,  which  is  the 
acidifying  principle.  And,  indeed,  the  word  oxygen  is  deriv- 
ed from  two  Greek  words,  signifying  to  produce  an  acid. 

Caroline.  Why,  then,  is  not  water,  which  contains  such  a 
quantity  of  oxygen,  acid  ? 

Mrs.  B.  Because  hydrogen,  which  is  the  other  constituent  of 
water,  is  not  susceptible  of  acidification. — I  believe  it  will  be 
necessary,  before  we  proceed  further,  to  say  a  few  words  of  the 
general  nature  of  acids,  though  it  is  rather  a  deviation  from  our 
plan  of  examining  the  simple  bodies  separately,  before  we  con- 
sider them  in  a  state  of  combination. 


1:2(3  SULPHUR. 

Acids  may  be  considered  as  a  peculiar  class  of  burnt*  bodies, 
which  during  their  combustion,  or  combination  with  oxygen, 
have  acquired  very  characteristic  properties.  They  are  chiefly 
discernible  by  their  sour  taste,  and  by  turning  red  most  of  the 
blue  vegetable  colours.  These  two  properties  are  common  to 
the  whole  class  of  acids  ;  but  each  of  them  is  distinguished  by 
other  peculiar  qualities.  Every  acid  consists  of  some  particular 
substance,  (which  constitutes  its  basis,  and  is  different  in  each,) 
and  of  oxygen,  which  is  common  to  them  all. 

Emily  But  I  do  not  clearly  seethe  difference  between  acids 
and  oxyds. 

Mrs.  B.  Acids  were,  in  fact,  oxyds,  which,  by  the  addition 
of  a  sufficient  quantity  of  oxygen,  have  been  converted  into 
acids.  For  acidification,  you  must  observe,  always  implies 
previous  oxydation,  as  a  body  must  have  combined  with  the 
quantity  of  oxygen  requisite  to  constitute  it  an  oxyd,  before  it 
can  combine  with  the  greater  quantity  which  is  necessary  to 
render  it  an  acid. 

Caroline.  Are  all  oxyds  capable  of  being  converted  into 
acids  ? 

Mrs.  B.  Very  far  from  it ;  it  is  only  certain  substances  which 
will  enter  into  that  peculiar  kind  of  union  with  oxygen  that  pro- 
duces acids,  and  the  number  of  these  is  proportionally  very 
small  ;  but  all  burnt  bodies  may  be  considered  as  belonging  ei- 
ther to  the  class  of  oxyds,  or  to  that  of  acids.  At  a  future  pe- 
riod, we  shall  enter  more  at  large  into  this  subject.  At  present, 
I  have  but  one  circumstance  further  to  point  out  to  your  obser- 
vation respecting  acids :  it  is,  that  most  of  them  are  suscepti- 
ble of  two  degrees  of  acidification,  according  to  the  different 
quantities  of  oxygen  with  which  their  basis  combines. 

Emily.  And  how  are  these  two  degrees  of  acidification  dis- 
tinguished ? 

Mrs.  B.  By  the  peculiar  properties  which  result  from  them. 
The  acid  we  have  just  made  is  the  first  or  weakest  degree  of 
acidification,  and  is  called  sulphureous  acid ;  if  it  were  fully 
saturated  with  oxygen,  it  would  be  called  sulphuric  acid.  You 
must  therefore  remember,  that  in  this,  as  in  all  acids,  the  first 
degree  of  acidification  is  expressed  by  the  termination  in  ous  : 
the  stronger,  by  the  termination  m  ic. 

Caroline.  And  how  is  the  sulphuric  acid  made  ? 

*  This  might  mislead  the  student.  Tlif  acids  am  not  all  of  them 
form  PC!  by  bunau^.  AH  th<->  vogvt^ble  aciiU.  as  theatric,  malic,  £e. 
exist  ready  formed  ;  some  of  th;:m  are  contained  in  fruits,  as  in  lo- 
apples,  &c.  C. 


SULPHUR.  I2t 

Mrs.  B.  By  burning  sulphur  in  pure  oxygen  gas,  and  thus 
rendering  its  combustion  much  more  complete.  I  have  provi- 
ded some  oxygen  gas  for  this  purpose  ;  it  is  in  that  bottle,  but 
we  must  first  decant  the  gas  into  the  glass  receiver  which  stands 
on  the  shelf  in  the  bath,  and  is  full  of  water. 

Caroline.  Pray,  let  me  try  to  do  it,  iMrs.  B. 

Mr*.  B.  It  requires  some  little  dexterity — hold  the  bottle 
completely  under  water,  and  do  not  turn  the  mouth  upwards, 
till  it  is  immediately  under  the  aperture  in  the  shelf,  through 
which  the  gas  is  to  pass  into  the  receiver,  and  then  turn 
it  up  gradually. — Very  well,  you  have  only  let  a  few  bub- 
bles escape,  and  that  must  be  expected  at  first  trial.  Now  I 
shall  put  this  piece  of  sulphur  into  the  receiver,  through  the 
opening  at  the  top,  and  introduce  along  with  it  a  small  piece  of 
lighted  tinder  to  set  fire  to  it. — This  requires  being  done  very 
quickly,  lest  the  atmospherical  air  should  get  in,  and  mix  with 
the  pure  oxygen  gas. 

Emily.  How  beautifully  it  burns  ! 

Caroline.  But  it  is  already  buried  in  the  thick  vapour.  This, 
I  suppose,  is  sulphuric  acid  ? 

Emily.  Are  these  acids  always  in  a  gaseous  state  ? 

Mrs.  B.  Sulphureous  acid,  as  we  have  already  observed,  is  a 
permanent  gas,  and  can  be  obtained  in  a  liquid  form  only  by 
condensing  it  in  water.  In  its  pure  state,  the  sulphureous  acid 
is  invisible,  and  it  now  appears  in  the  form  of  a  white  smoke, 
from  its  combining  with  the  moisture.  But  the  vapour  of  sul- 
phuric acid,  which  you  have  just  seen  to  rise  during  the  com- 
bustion, is  not  a  gas,  but  only  a  vapour,  which  condenses  into 
liquid  sulphuric  acid,  by  losing  its  caloric.  But  it  appears  from 
Sir  H.  Davy's  experiments,  that  this  formation  apd  condensa- 
tion of  sulphuric  acid  requires  the  presence  of  water,  for  which 
purpose  the  vapour  is  received  into  cold  water  which  may  after- 
wards be  separated  from  the  acid  by  evaporation. 

Sulphur  has  hitherto  been  considered  as  a  simple  substance; 
but  Sir  H.  Davy  has  suspected  that  it  contains  a  small  portion 
of  hydrogen,  and  perhaps  also  of  oxygen. 

On  submitting  sulphur  to  the  action  of  the  Voltaic  battery, 
he  observed  that  the  negative  wire  gave  out  hydrogen ;  and  the 
existence  of  hydrogen  in  sulphur  was  rendered  still  more  proba- 
ble by  his  observing  that  a  small  quantity  of  water  was  produ- 
ced during  the  combustion  of  sulphur. 

Emily.  And  pray  of  what  nature  is  sulphur  when  perfectly 
pure? 

Mrs.  B.  Sulphur  has  probably  never  been  obtained  perfectly 
free  from  combination,  so  that  its  radical  may  possibly  possess 

12 


122  SULPHUR. 

properties  very  different  from  those  of  common  sulphur.  It 
has  been  suspected  to  be  of  a  metallic  nature  5  but  this  is  mere 
conjecture. 

Before  we  quit  the  subject  of  sulphur,  I  must  tell  you  that  it 
is  susceptible  of  combining  with  a  great  variety  of  substances, 
and  especially  with  hydrogen,  with  which  you  are  already  ac- 
quainted. Hydrogen  gas  can  dissolve  a  small  portion  of  it. 

Emily.  What !  can  a  gas  dissolve  a  solid  substance  ? 

Mrs.  B.  Yes  5  a  solid  substance  may  be  so  minutely  divided 
by  heat,  as  to  become  soluble  in  gas  :  and  there  are  several  in- 
stances of  it.  But  you  must  observe,  that,  in  this  case,  a  chem- 
ical union  or  combination  of  the  sulphur  with  the  hydrogen 
gas  is  produced.  In  order  to  effect  this,  the  sulphur  must  be 
strongly  heated  in  contact  with  the  gas  ;  the  heat  reduces  the 
sulphur  to  such  a  state  of  extreme  division,  and  diffuses  it  so 
thoroughly  through  the  gas7  that  they  combine  and  incorporate 
together.  And  as  a  proof  that  there  must  be  a  chemical  union 
between  the  sulphur  and  the  gas,  it  is  sufficient  to  remark  that 
they  are  not  separated  when  the  sulphur  loses  the  caloric  by 
which  it  was  volatilized.  Besides,  it  is  evident,  from  the  pecu- 
liar fetid  smell  of  this  gns,  that  it  is  a  new  compound  totally  dif- 
ferent from  either  of  its  constituents  ;  it  is  called  sulphuretted 
hydrogen  gas,  and  is  contained  in  great  abundance  in  sulphu- 
reous mineral  waters. 

Caroline.  Are  not  the  Harrogate  waters  of  this  nature  ? 

Mrs.  B.  Yes  ;  they  are  naturally  impregnated  with  sulphu- 
retted hydrogen  gas,  and  there  are  many  other  springs  of  the 
Same  kind,  which  shows  that  this  gas  must  often  be  formed  in 
the  bowels  of  the  earth  by  spontaneous  processes  of  nature. 

Caroline.  And  could  not  such  waters  be  made  artificially  by 
impregnating  common  water  with  this  gas? 

Mrs.  B.  Yes ;  they  can  be  so  well  imitated,  as  perfectly  to 
resemble  the  Hai  rogate  waters. 

Sulphur  combines  likewise  with  phosphorus,  and  with  the  al- 
kalies, and  alkaline  earths,  substances  with  which  you  are  yet 
unacquainted.  We  cannot,  therefore,  enter  into  these  combi- 
nations at  present.  In  our  next  lesson  we  shall  treat  of  phos* 
phorus. 

Emily.  May  we  not  begin  that  subject  to-day  ;  this  lesson 
has  been  so  short  ? 

Mrs.  B.  I  have  no  objection,  if  you  are  not  tired.  What  do 
you  say,  Caroline? 

Caroline.  \  am  as  desirous  as  Emily  of  prolonging  the  lesson 
to-day,  especially  as  we  are  to  enter  on  a  new  subject ;  for  I 
confess  that  sulphur  has  not  appeared  to  me  so  interesting  as 
the  other  simple  bodies. 


PHOSPHORUS.  123 

Mrs.  B.  Perhaps  you  may  find  phosphorus  more  entertain- 
ing. You  must  not,  however,  be  discouraged  when  you  meet 
with  some  parts  of  a  study  less  amusing  than  others  ;  it  would 
answer  no  good  purpose  to  select  the  most  pleasing  parts,  since, 
it"  we  did  not  proceed  with  some  method,  in  order  to  acquire  a 
general  idea  of  the  whole,  we  could  scarcely  expect  to  take  in- 
terest in  any  particular  subjects. 

PHOSPHORUS. 

PHOSPHORUS  is  considered  as  a  simple  body  ;  though,  like 
sulphur,  it  has  been  suspected  of  containing  hydrogen.  It  was 
not  known  by  the  earlier  chemists.  It  was  first  discovered  by 
Brandt,  a  chemist  of  Hamburgh,  whilst  employed  in  researches 
after  the  philosopher's  stone  ;  but  the  method  of  obtaining  it  re- 
mained a  secret  till  it  was  a  second  time  discovered  both  by 
Kunckel  and  Boyle,  in  the  year  1680.  You  see  a  specimen  of 
phosphorus  in  this  phial ;  it  is  generally  moulded  into  small 
sticks  of  a  yellowish  colour,  as  you  find  it  here. 

Caroline.  I  do  not  understand  in  what  the  discovery  consist- 
ed ;  there  may  be  a  secret  method  of  making  an  artificial  com- 
position, but  how  can  you  talk  of  making  a  substance  which 
naturally  exists  ? 

Mrs.  B.  A  body  may  exist  in  nature  so  closely  combined 
with  other  substances,  as  to  elude  the  observation  of  chemists, 
or  render  it  extremely  difficult  to  obtain  it  in  its  separate  state. 
This  is  the  case  with  phosphorus,  which  is  always  so  intimate- 
ly combined  with  other  substances,  that  its  existence  remained 
unnoticed  till  Brandt  discovered  the  means  of  obtaining  it  free 
from  other  combinations.  It  is  found  in  all  animal  substances, 
and  is  now  chiefly  extracted  from  bones,  by  a  chemical  process. 
I:  exists  also  in  some  plants,  that  bear  a  strong  analogy  to  ani- 
mal matter  in  their  chemical  composition. 

Emily.  But  is  it  never  found  in  its  pure  separate  state  ? 

Mrs.  B.  Never,  and  this  is  the  reason  that  it  remained  so 
long  undiscovered* 

Phosphorus  is  eminently  combustible  ;  it  meltsand  takes  fire 
at  the  temperature  of  one  hundred  degrees,  and  absorbs  in  its 
combustion  nearly  once  and  a  half  its  own  weight  of  oxygen. 

Caroline.  What !  will  a  pound  of  phosphorus  consume  & 
pound  and  a  half  of  oxygen  ? 

Mrs.  B.  So  it  appears  from  accurate  experiments.  I  can 
show  you  with  what  violence  it  combines  with  oxygen,  by  burn- 
ing some  of  it  in  that  gas.  We  must  manage  the  experiment 
in  the  same  manner  as  we  did  the  combustion  of  sulphur.  Von 


124  PHOSPHORUS. 

see  I  am  obliged  to  cut  this  little  bit  of  phosphorus  under  wa- 
ter, otherwise  there  would  be  danger  of  its  taking  fire  by  the 
heat  of  my  fingers.  I  now  put  it  into  the  receiver,  and  kindle 
it  by  means  of  a  hot  wire. 

Emily.  What  a  blaze !  I  can  hardly  look  at  it.  I  never  saw 
any  thing  so  brilliant.  Does  it  not  hurt  your  eyes,  Caroline  ? 

Caroline.  Yes  ;  but  still  1  cannot  help  looking  at  it.  A 
prodigious  quantity  of  oxygen  must  indeed  be  absorbed,  when 
so  much  light  and  caloric  are  disengaged  ! 

Mrs.  B.  In  the  combustion  of  a  pound  of  phosphorus,  a  suf- 
ficient quantity  of  caloric  is  set  free  to  melt  upwards  of  a  hun- 
dred pounds  of  ice  5  this  has  been  computed  by  direct  experi- 
ments with  the  calorimeter. 

Emily.  And  is  the  result  of  this  combustion,  like  that  of  sul- 
phur, an  acid  ? 

Mrs.  B.  Yes  ;  phosphoric  acid.  And  had  we  duly  propor- 
tioned the  phosphorus  and  the  oxygen,  they  would  have  been 
completely  converted  into  phosphoric  acid,  weighing  together, 
in  this  new  state,  exactly  the  sum  of  their  weights  separately. 
The  water  would  have  ascended  into  the  receiver,  on  account 
of  the  vacuum  formed,  and  would  have  filled  it  entirely.  In 
this  case,  as  in  the  combustion  of  sulphur,  the  acid  vapour  form- 
ed is  absorbed  and  condensed  in  the  water  of  the  receiver.  But 
when  this  combustion  is  performed  without  any  water  or  mois* 
lure  being  present,  the  acid  then  appears  in  the  form  of  con- 
crete whitish  flakes,  which  are,  however,  extremely  ready  to 
melt  upon  the  least  admission  of  moisture. 

Emily.  Does  phosphorus,  in  burning  in  atmospherical  air2 
produce,  like  sulphur,  a  weaker  sort  of  the  same  acid  ? 

Mrs.  B.  No :  for  it  burns  in  atmospherical  air,  nearly  at  the 
same  temperature  as  in  pure  oxygen  gas  ;  and  it  is  in  both  ca- 
ses so  strongly  disposed  to  combine  with  the  oxygen,  that  the 
combustion  is  perfect,  and  the  product  similar ;  only  in  atmos- 
pherical air,  being  less  rapidly  supplied  with  oxygen,  the  pro~ 
eess  is  performed  in  a  slow  manner. 

Caroline.  But  is  there  no  method  of  acidifying  phosphorus 
in  a  slighter  manner,  so  as  to  form  phosphorous  acid.? 

Mrs.  B.  Yes,  there  is.  When  simply  exposed  to  the  atmos- 
phere, phosphorus  undergoes  a  kind  of  slow  combustion  at  any 
temperature  above  zero. 

Emily.  Is  not  the  process  in  this  case  rather  an  oxydation 
than  a  combustion  ?  For  if  the  oxygen  is  too  slowly  absorbed 
for  a  sensible  quantity  of  light  and  heat  to  be  disengaged,  it  is 
not  a  true  combustion. 

Mrs.  B.  The  case  is  not  as  you  suppose  :  a  faint  light  is 


I»«OSPHORUS*  125 

emitted  which  is  very  discernible  in  the  dark ;  but  the  heai 
evolved  is  not  sufficiently  strong  to  be  sensible;  a  whitish  va- 
pour arises  from  this  combustion,  which,  uniting  with  water, 
condenses  into  liquid  phosphorus  acid. 

Caroline.  Is  it  not  very  singular  that  phosphorus  should 
burn  at  so  low  a  temperature  in  atmospherical  air,  whilst  it 
does  not  burn  in  pure  oxygen  without  the  application  of  heat  ? 

Mrs.  B.  So  it  at  first  appears.  But  this  circumstance  seems 
to  be  owing  to  the  nitrogen  gas  of  the  atmosphere.  This  gas 
dissolves  small  particles  of  phosphorus,  which  being  thus  mi- 
nutely divided  and  diffused  in  the  atmospherical  air,  combines 
with  the  oxygen,  and  undergoes  this  slow  combustion.  But  the 
same  effect  does  not  take  place  in  oxygen  gas,  because  it  is  not 
capable  of  dissolving  phosphorus  ;  it  is  therefore  necessary,  in 
this  case,  that  heat  should  be  applied  to  effect  that  division  of 
particles,  which,  in  the  former  instance,  is  produced  by  the  ni- 
trogen. 

Emily.  I  have  seen  letters  written  with  phosphorus,  which 
are  invisible  by  day-light,  but  may  be  read  in  the  dark  by  their  ^ 
own  light.     They  look  as  if  they  were  written  with  fire  j  yet 
they  do  not  seem  to  burn. 

Mrs.  B.  But  they  do  really  burn ;  for  it  is  by  their  slow  com- 
bustion that  the  light  is  emitted ;  and  phosphorus  acid  is  the  re- 
sult of  this  combustion. 

Phosphorus  is  sometimes  used  as  a  test  to  estimate  the  puri- 
ty of  atmospherical  air.  For  this  purpose,  it  is  burnt  in  a  gra- 
duated tube,  called  an  Eudiometer  (PLATE  XI.  fig.  2.),  and 
from  the  quantity  of  air  which  the  phosphorus  absorbs,  the  pro- 
portion of  oxygen  in  the  air  examined  is  deduced ;  for  the  phos- 
phorus will  absorb  all  the  oxygen,  and  the  nitrogen  alone  will 
remain. 

Emily.  And  the  more  oxygen  is  contained  in  the  atmosphere^ 
the  purer,  I  suppose,  it  is  esteemed  ? 

Mrs.  B.  Certainly.  Phosphorus,  when  melted,  combines 
with  a  great  variety  of  substances.  With  sulphur  it  forms  a 
compound  so  extremely  combustible,  that  it  immediately  takes 
fire  on  coming  m  contact  with  the  air.  It  is  with  this  compo- 
sition  that  phosphoric  matches  are  prepared,  which  kindle  as 
soon  as  they  are  taken  out  of  their  case  and  are  exposed  to  the 
air. 

Emily.  I  have  a  box  of  these  curious  matches  ;  but  I  have 
observed,  that  in  very  cold  weather,  they  will  not  take  fire 
without  being  previously  rubbed. 

Jtfrs.  '3.  By  rubbing  them  you  raise  their  temperature  5  for? 
you  knowj  friction  is  one  of  thf  means  of  extrcating  heat, 

12* 


126  PHOSPHORUS. 

Emily.  Will  phosphorus  combine  with  hydrogen  gas,  as  sul- 
phur does  ?  , 

Mrs.  B.  Yes;  and  the  compound  gas  which  results  from 
this  combination  has  a  smell  still  more  fetid  than  the  sulphuret- 
ted hydrogen  ;  it  resembles  that  of  garlic. 

The  phospkoretted  hydrogen  gas  has  this  remarkable  pecul- 
iarity, that  it  takes  fire  spontaneously  in  the  atmosphere,  at  any 
temperature.  It  is  thus,  probably,  that  are  produced  those 
transient  flames,  or  flashes  of  light,  called  by  the  vulgar  Will- 
of-the-Whisp)  or  more  properly  Ignesfatvi,  which  are  often 
seen  in  church-yards,  and  places  where  the  putrefactions  of 
animal  matter  exhale  phosphorus  and  hydrogen  gas. 

Caroline.  Country  people,  who  are  so  much  frightened  by 
those  appearances,  would  soon  be  reconciled  to  them,  if  they 
knew  from  what  a  simple  cause  they  proceed. 

Mrs.  B.  There  are  other  combinations  of  phosphorus  that 
have  also  very  singular  properties,  particularly  that  which  re- 
sults from  its  union  with  lime. 

Emily.  Is  there  any  name  to  distinguish  the  combination  of 
two  substances,  like  phosphorus  and  lime,  neither  of  which 
are  oxygen,  and  which  cannot  therefore  produce  either  an  ox- 
yd  or  an  acid  ? 

Mrs.  B.  The  names  of  such  combinations  are  composed  from 
those  of  their  ingredients,  merely  from  a  slight  change  in  their 
termination.  Thus  the  combination  of  sulphur  with  lime  is 
called  a  sulphuret,  and  that  of  phosphorus,  a  phosphuret  of 
lime.*  This  latter  compound,  I  was  going  to  say,  has  the  sin- 
gular property  of  decomposing  water,  merely  by  being  thrown 
into  it.  It  effects  this  by  absorbing  the  oxygen  of  water,  in 
consequence  of  which  bubbles  of  hydrogen  gas  ascend,  holding 
in  solution  a  small  quantity  of  phosphorus. 

*  Phosphuret  of  lime  is  a  very  curious  substance.  To  make  it, 
take  a  thin  glass  tube,  6  or  8  inches  long,  and  less  than  half  an  inch 
in  diameter  ;  if  it  is  closed  at  one  end,  so  much  the  better,  but  a  cork 
will  do.  Near  the  closed  end  put  a  piece  of  phosphorus  half  an  inch 
long.  Then  put  in  by  means  of  a  stick  or  wire,  holding  the  tube  hori- 
zontally, thirty  or  forty  pieces  of  newly  burned  quick-lime,  about  the 
size  of  split  peas,  letting  the  lowest  remain  2  or  3  inches  from  the  phos- 
phorus. Then  stop  the  other  end  of  the  tube  loosely,  and  place  the 
part  containing  the  quick-lime,  in  a  bed  of  charcoal,  so  contriving  it 
that  a  candle  or  red  hot  iron  can  be  brought  under  the  part  where  the 
phosphorus  lies.  Kindle  a  fire  by  means  of  bellows,  and  heat  the  lime 
red  hot,  without  melting  the  phosphorus,  which  may  be  kept  cool  by  a 
wet  rag ;  when  this  is  done,  bring  the  hot  iron  or  candle  under  the 
phosphorus,  so  as  to  make  it  pass  through  the  quick-lime  in  the  form 
of  vapour.  Cork  up  the  phosphuret  of  lime  for  use.  C, 


PHOSPHORUS.  127 

Emily.  These  bubbles  then  are  phosphoretted  hydrogen 
gas  ? 

Mrs.  B.  Yes  ;  and  they  produce  the  singular  appearance  of 
a  flash  of  fire  issuing  from  the  water,  as  the  bubbles  kindle  and 
detonate  on  the  surface  of  the  water,  at  the  instant  that  they 
come  in  contact  with  the  atmosphere.  [If  the  water  is  icarm, 
the  experiment  is  more  apt  to  succeed.  C.] 

Caroline.  Is  not  this  effect  nearly  similar  to  that  produced 
by  the  combination  of  phosphorus  and  sulphur,  or,  more  pro- 
perly speaking,  the phosphuret  of  sulphur? 

Mrs.  B.  Yes  ;  but  the  phenomenon  appears  more  extraordi- 
nary in  this  case,  from  the  presence  of  water,  and  from  the 
gaseous  form  of  the  combustible  compound.  Besides,  the  ex- 
periment surprises  by  its  great  simplicity.  You  only  throw  a 
piece  of  phosphuret  of  lime  into  a  glass  of  water,  and  bubbles 
of  fire  will  immediately  issue  from  it. 

Caroline.  Cannot  we  try  the  experiment  ? 

Mrs.  B.'  Very  easily  ;  but  we  must  do  it  in  the  open  air  ;  for 
the  smell  of  the  phosphoretted  hydrogen  gas  is  so  extremely  fe- 
tid, that  it  would  be  intolerable  in  the  house.  But  before  we 
leave  the  room,  we  may  produce,  by  another  process,  some 
bubbles  of  the  same  gas,  which  are  much  less  offensive. 

There  is  in  this  little  glass  retort  a  solution  of  potash  in  wa- 
ter $  I  add  to  it  a  small  piece  of  phosphorus.  We  must  now 
heat  the  retort  over  the  lamp,  after  having  engaged  its  neck 
under  water — You  see  it  begins  to  boil  ;  in  a  few  minutes  bub- 
bles will  appear,  which  take  fire  and  detonate  as  they  issue  from 
the  water. 

Caroline.  There  is  one — and  another.  How  curious  it  is  .' 
— But  I  do  not  understand  how  this  is  produced. 

Mrs.  B.  It  is  the  consequence  of  a  display  of  affinities  too 
complicated,  I  fear,  to  be  made  perfectly  intelligible  to  you  at 
present. 

In  a  few  words,  the  reciprocal  action  of  the  potash,  phos- 
phorus, caloric,  and  water,  are  such,  that  some  of  the  water 
is  decomposed,  and  the  hydrogen  gas  thereby  formed  carries 
off  some  minute  particles  of  phosphorus,  with  which  it  forms 
phosphoretted  hydrogen  gas,  a  compound  which  spontaneously 
takes  fire  at  almost  any  temperature. 

Emily.  What  is  that  circular  ring  of  smoke  which  slowly  ri- 
ses from  each  bubble  after  its  detonation  ? 

Mrs.  B.  It  consists  of  water  and  phosphoric  acid  in  vapour; 
which  are  produced  by  the  combustion  of  hydrogen  and  phos- 
phorus. 


128  CARBON. 

CONVERSATION  IX. 

ON  CARBOS. 

Caroline.  TO-DAY,  Mrs.  B.,  I  believe  we  are  to  learn  the 
nature  and  properties  of  CARBON.  This  substance  is  quite  new 
to  me ;  I  never  heard  it  mentioned  before. 

Mrs.  B.  Not  so  new  as  you  imagine  ;  for  carbon  is  nothing 
more  than  charcoal  in  a  state  of  purity,  that  is  to  say,  unmix- 
ed with  any  foreign  ingredients. 

Caroline.  But  charcoal  is  made  by  art,  Mrs.  B.,  and  a  body 
consisting  of  one  simple  substance  cannot  be  fabricated  ? 

Mrs.  B.  You  again  confound  the  idea,  of  making  a  simple 
body,  with  that  of  separating  it  from  a  compound.  The  che- 
mical processes  by  which  a  simple  body  is  obtained  in  a  state  of 
purity,  consist  in  unmaking  the  compound  in  which  it  is  con- 
tained, in  order  to  separate  from  it  the  simple  substance  in 
question.  The  method  by  which  charcoal  is  usually  obtained, 
is,  indeed,  commonly  called  making  it ;  but,  upon  examina- 
tion, you  will  find  this  process  to  consist  only  in  separating  it 
from  other  substances  with  which  it  is  found  combined  in  na- 
ture. 

Carbon  forms  a  considerable  part  of  the  solid  matter  of  all 
organised  bodies  ;  but  it  is  most  abundant  in  the  vegetable  cre- 
ation, and  it  is  chiefly  obtained  from  wood.  When  the  oil  and 
water  (which  are  other  constituents  of  vegetable  matter)  are 
evaporated,  the  black,  porous,  brittle  substance  that  remains, 
is  charcoal. 

Caroline.  But  if  heat  be  applied  to  the  wood  in  order  to 
evaporate  the  oil  and  water,  will  not  the  temperature  of  the 
charcoal  be  raised  so  as  to  make  it  burn  ;  and  if  it  combines 
with  oxygen,  can  we  any  longer  call  it  pure. 

Mrs.  B.  I  was  going  to  say,  that,  in  this  operation,  the  air 
must  be  excluded. 

Caroline.  How  then  can  the  vapour  of  the  oil  and  water  fiy 
off? 

Mrs.  B.  In  order  to  produce  charcoal  in  its  purest  state, 
(which  is,  even  then,  but  a  less  imperfect  sort  of  carbon,)  the 
operation  should  be  performed  in  an  earthen  retort.  Heat  be- 
ing applied  to  the  body  of  the  retort,  the  evaporable  part  of  the 
wood  will  escape  through  its  neck,  into  which  no  air  can  pene- 
trate as  long  as  the  heated  vapour  continues  to  fill  it.  And  if  it 
b»*  wished  to  collect  these  volatile  products  of  the  wood,  ihis 
can  easily  be  done  by  introducing  the  neck  of  the  retort  into  the 


CARBON. 


water-bath  apparatus,  with  which  you  are  acquainted.  But 
the  preparation  of  common  charcoal,  such  as  is  used  in  kitch- 
ens and  manufactures,  is  performed  on  a  much  larger  scale, 
and  by  an  easier  and  less  expensive  process. 

F.mily.  I  have  seen  the  process  of  making  common  charcoal. 
The  wood  is  ranged  on  the  ground  in  a  pile  of  a  pyramidical 
form,  with  a  fire  underneath  ;  the  whole  is  then  covered  wijh 
day,  a  few  holes  only  being  left  open  for  the  circulation  of  air. 

Mrs.  B.  The  holes  are  closed  as  soon  as  the  wood  is  fairly 
lighted,  so  that  the  combustion  is  checked,  or  at  least  contin- 
ues but  in  a  very  imperfect  manner  ;  but  the  heat  produced  by 
it  is  sufficient  to  force  out  and  volatilize,  through  the  earthy  co- 
ver, most  part  of  the  oily  and  watery  principles  of  the  wood, 
although  it  cannot  reduce  it  to  ashes. 

Emily.  Is  pure  carbon  as  black  as  charcoal  ? 

Mrs.  B.  The  purest  charcoal  we  can  prepare  is  so  ;  but 
chemists  have  never  yet  been  able  to  separate  it  entirely  from 
hydrogen.  Sir  H.  Davy  says,  that  the  most  perfect*  carbon 
that  is  prepared  by  art  contains  about  five  per  cent  of  hydro- 
gen ;  he  is  of  opinion,  that  if  we  could  obtain  it  quite  free 
from  foreign  ingredients,  it  would  be  metallic,  in  common  with 
other  simple  substances. 

But  there  is  a  form  in  which  charcoal  appears,  that  I  dare 
say  will  surprise  you.  —  This  ring,  which  I  wear  on  my  finger, 
owes  its  brilliancy  to  a  small  piece  of  carbon. 

Caroline.  Surely,  you  are  jesting,  Mrs.  B.  ? 

Emily.  I  thought  your  ring  was  diamond  ? 

Mrs.  B.  It  is  so.  But  diamond  is  nothing  more  than  carbon 
in  a  crystalizecl  state. 

Emily.  That  is  astonishing  !  Is  it  possible  to  see  two  things 
apparently  more  different  than  diamond  and  charcoal  ? 

Caroline.  It  is,  indeed,  curious  to  think  that  we  adorn  our- 
selves with  jewels  of  charcoal  ! 

Mrs.  B.  There  are  many  other  substances,  consisting  chiefly 
of  carbon,  that  are  remarkably  white.  Cotton,  for  instance,  is 
almost  wholly  carbon. 

Caroline.  That,  I  own,  I  could  never  have  imagined  !  —  But 
pray,  Mrs.  B.,  since  it  is  known  of  what  substance  diamond 
and  cotton  are  composed,  why  should  they  not  be  manufactur- 
ed, or  imitated,  by  some  chemical  process,  which  would  render 
them  much  cheaper,  and  more  plentiful  than  the  present  mode 
of  obtaining  them  ? 

Mrs.  .  You  might  as  well,  my  dear,  propose  that  we  should 
make  flowers  and  fruit,  nay,  perhaps  even  animals,  by  a  chem- 
kai  process  ;  for  it  is  known  of  what  these  bodies  consist,  since; 


130  CARBON. 

every  thing  which  we  are  acquainted  with  in  nature  is  formed 
from  the  various  simple  substances  that  we  have  enumerated. 
But  you  must  not  suppose  that  a  knowledge  of  the  component 
parts  of  a  body  will  in  every  case  enable  us  to  imitate  it.  It  is 
much  less  difficult  to  decompose  bodies,  and  discover  of  what 
materials  they  are  made,  than  it  is  to  recompose  them.  The 
first  of  these  processes  is  called  analysis,  the  last  synthesis. 
When  we  are  able  to  ascertain  the  nature  of  a  substance  by 
both  these  methods,  so  that  the  result  of  one  confirms  that  of 
the  other,  we  obtain  the  most  complete  knowledge  of  it  that 
we  are  capable  of  acquiring.  This  is  the  case  with  water,  with 
the  atmosphere,  with  most  of  the  oxyds,  acids,  and  neutral 
salts,  and  with  many  other  compounds.  But  the  more  com- 
plicated combinations  of  nature,  even  in  the  mineral  kingdom, 
are  in  general  beyond  our  reach,  and  any  attempt  to  imitate  or- 
ganised bodies  must  ever  prove  fruitless ;  their  formation  is  a 
secret  tjiat  rests  in  the  bosom  of  the  Creator.  You  see,  there- 
fore, ho*v  vain  it  would  be  to  attempt  to  make  cotton  by  chemi- 
cal means.  But,  surely,  we  have  no  reason  to  regret  our  ina- 
bility in  this  instance,  when  nature  has  so  clearly  pointed  out  a 
method  of  obtaining  it  in  perfection  and  abundance. 

Caroline.  I  did  not  imagine  that  the  principle  of  life  could 
be  imitated  by  the  aid  of  chemistry  ;  but  it  did  not  appear  to 
me  absurd  to  suppose  that  chemists  might  attain  a  perfect  imi- 
tation of  inanimate  nature. 

Mrs.  B.  They  have  succeeded  in  this  point  in  a  variety  of 
instances;  but,  as  you  justly  observe,  the  principle  of  life,  or 
even  the  minute  and  intimate  organisation  of  the  vegetable 
kingdom,  are  secrets  that  have  almost  entirely  eluded  the  re- 
searches of  philosophers;  nor  do  I  imagine  that  human  art  will 
ever  be  capable  of  investigating  them  with  complete  success. 

Emily.  But  diamond,  since  it  consists  of  one  simple  unor- 
ganised substance,  might  be,  one  would  think,  perfectly  imitable 
by  art  r 

Mrs.  B.  It  is  sometimes  as  much  beyond  our  power  to  ob- 
tain a  simple  body  in  a  state  of  perfect  purity,  as  it  is  to  imi- 
tate a  complicated  combination ;  for  the  operations  by  which 
nature  separates  bodies  are  frequently  as  inimitable  as  those 
which  she  uses  for  their  combination.  This  is  the  case  with 
carbon;  all  the  efforts  of  chemists  to  separate  it  entirely  from 
other  substances  have  been  fruitless,  and  in  the  purest  state  in 
which  it  can  be  obtained  by  art,  it  still  retains  a  portion  of  hy- 
drogen, and  probably  of  some  other  foreign  ingredients.  We 
are  ignorant  or  the  m^ans  which  nature  employs  tojcrystalize  it. 
It  may  probably  be  the  work  of  ages,  to  purify,  arrange,  and 


CARBON.  131 

unite  the  particles  of  carbon  in  the  form  of  diamond.  Here  is 
some  charcoal  in  the  purest  state  we  can  procure  it ;  you  see 
that  it  is  a  very  black,  brittle,  light,  porous  substance,  entirely 
destitute  of  either  taste  or  smell.  Heat,  without  air,  produces 
no  alteration  in  it,  as  it  is  not  volatile ;  but,  on  the  contrary,  it 
invariably  remains  at  the  bottom  of  the  vessel  after  all  the  oth- 
er parts  of  the  vegetable  are  evaporated. 

Emily.  Yet  carbon  is,  no  doubt,  combustible,  since  you  say 
that  charcoal  would  absorb  oxygen  if  air  were  admitted  during 
its  preparation  ? 

Caroline.  Unquestionably.  Besides,  you  know,  Emily,  how 
much  it  is  used  in  cooking.  But  pray  what  is  the  reason  that 
charcoal  burns  without  smoke,  whilst  a  wood  fire  smokes  so 
much  ? 

Mrs.  B.  Because,  in  the  conversion  of  wood  into  charcoal, 
the  volatile  particles  of  the  former  have  been  evaporated. 

Caroline.  Yet  I  have  frequently  seen  charcoal  burn  with 
flame  ;  therefore  it  must,  in  that  case,  contain  some  hydrogen. 

Mrs.  B.  Very  true  ;  but  you  should  recollect  that  charcoal, 
especially  that  which  is  uled  for  common  purposes,  is  not  per- 
fectly pure.  It  generally  retains  some  remains  of  the  various 
other  component  parts  of  vegetables,  and  hydrogen  particular- 
ly, which  accounts  for  the  flame  in  question. 

Caroline.  But  what  becomes  of  the  carbon  itself  during  its 
combustion  ? 

Mrs.  B.  It  gradually  combines  with  the  oxygen  of  the  atmos- 
phere, in  the  same  way  as  sulphur  and  phosphorus,  and,  like 
those  substances,  it  is  converted  into  a  peculiar  acid,  which  flies 
off  in  a  gaseous  form.  There  is  this  difference,  however,  that 
the  acid  is  not,  in  this  instance,  as  in  the  two  cases  just  men- 
tioned, a  mere  condensible  vapour,  but  a  permanent  elastic  flu- 
id, which  always  remains  in  the  state  of  gas,  under  any  pres- 
sure and  at  any  temperature.  The  nature  of  this  acid  was  first 
ascertained  by  Dr.  Black,  of  Edinburgh  ;  and,  before  the  intro- 
duction of  the  new  nomenclature,  it  was  called  Jixed  air.  It 
is  now  distinguished  by  the  more  appropriate  name  of  carbonic 
acid  gas. 

Emily.  Carbon  then,  can  be  volatilized  by  burning,  though, 
by  heat  alone,  no  such  effect  is  produced  ? 

Mrs.  B.  Yes ;  but  then  it  is  no  longer  simple  carbon,  but  an 
acid  of  which  carbon  forms  the  basis.  In  this  state,  carbon  re- 
tains no  more  apearance  of  solidity  or  coporeal  form,  than  the 
basis  of  any  other  gas.  And  you  may,  I  think,  from  this  in- 
stance, derive  a  more  clear  idea  of  the  basis  of  the  oxygen,  hy- 
'trogen,  and  nitrogen  gases,  the  existence  of  which,  as  real  bo* 


132  CARBON. 

dies,  you  seemed  to  doubt,  because  they  were  not  to  be  obtain- 
ed simply  in  a  solid  form. 

Emily.  That  is  true ;  we  may  conceive  the  basis  of  the  oxy- 
gen, and  of  the  other  gases,  to  be  solid,  heavy  substances,  like 
cai  bors ;  but  so  much  expanded  by  caloric  as  to  become  invisible. 

Caroline.  But  does  not  the  carbonic  acid  gas  partake  of  the 
blackness  of  charcoal  ? 

Mrs.  B.  Not  in  the  least.  Blackness,  you  know,  does  not 
appear  to  be  essential  to  carbon,  and  it  is  pure  carbon,  and  not 
charcoal,  that  we  must  consider  as  the  basis  of  carbonic  acid. 
We  shall  make  some  carbonic  acid,  and,  in  order  to  hasten  the 
process,  we  shall  burn  the  carbon  in  oxygen  gas. 

Emily.   But  do  you  mean  then  to  burn  diamond  ? 

Mrs.  B.  Charcoal  will  answer  the  purpose  still  better,  being 
softer  and  more  easy  to  inflame;  besides  the  experiments  on 
diamond  are  rather  expensive. 

Caroline.  But  is  it  possible  to  burn  diamond? 

Mrs.  B.  Yes,  it  is;  and  in  order  to  effect  this  combustion, 
nothing  more  is  required  than  to  apuly  a  sufficient  degree  of 
heat  by  means  of  the  blow-pipe,  and  of  a  stream  of  oxygen  gas. 
Indeed  it  is  by  burning  diamond  that  its  chemical  nature  has 
been  ascertained.  It  has  long  been  known  as  a  combustible 
substance,  but  it  is  within  these  few  years  only  that  the  product 
of  its  combustion  has  been  proved  to  be  pure  carbonic  acid. 
This  remarkable  discovery  is  due  to  Mr.  Tennant. 

Now  let  us  try  to  make  some  carbonic  acid. — Will  you, 
Emily,  decant  some  oxygen  gas  from  this  large  jar  into  the  re- 
ceiver in  which  we  are  to  burn  the  carbon  ;  and  I  shall  intro- 
duce this  small  piece  of  charcoal,  with  a  little  lighted  tinder, 
which  will  be  necessary  to  give  the  first  impulse  to  the  com- 
bustion. 

Emily.  I  cannot  conceive  how  so  small  a  piece  of  tinder,  and 
that  but  just  lighted,  can  raise  the  temperature  of  the  carbon 
sufficiently  to  set  fire  to  it :  for  it  can  produce  scarcely  any  sen- 
sible heat,  and  it  hardly  touches  the  carbon. 

Mrs.  B.  The  tinder  thus  kindled  has  only  heat  enough  to  be- 
gin its  own  combustion,  which,  however,  soon  becomes  so  rap- 
id in  the  oxygen  gas,  as  to  raise  the  temperature  of  the  char- 
coal sufficiently  for  this  to  burn  likewise,  as  you  see  is  now  the 
case. 

Emily.  lam  surprised  that  the  combustion  of  carbon  is  not 
more  brilliant ;  it  does  not  give  out  n«'ar  so  much  light  or  caloric 
as  phosphorus,  or  sulphur  Yetsinre  it  combines  with  so  muck 
oxygen,  why  is  not  4  proportional  quantity  of  light  and  heat 


CARBO.N.  133 

disengaged  from  tiie  decomposition  of  the  oxygen  gas,  and  the 
union  of  its  electricity  with  that  of  the  charcoal  ? 

Mrs.  B.  It  is  not  surprising  that  less  light  and  heat  should 
be  liberated  in  this  than  in  almost  any  other  combustion,  since 
the  oxygen,  instead  of  entering  into  a  solid  or  liquid  combina- 
tion, as  it  does  in  the  phosphoric  and  sulphuric  acids,  is  em- 
ployed in  forming  another  elastic  fluid  ;  it  therefore  parts  with 
less  of  its  caloric. 

Emily.  True;  and,  on  second  consideration,  it  appears,  on 
the  contrary,  surprising  that  the  oxygen  should,  in  its  combina- 
tion with  carbon,  retain  a  sufficient  portion  of  caloric  to  main- 
tain both  substances  in  a  gaseous  state. 

Caroline.  We  may  then  judge  of  the  degree  of  solidity  in 
which  oxygen  is  combined  in  a  burnt  body,  by  the  quantity  of 
caloric  liberated  during  its  combustion  ? 

Mrs.  B.  Yes  5  provided  that  you  take  into  the  account  the 
quantity  of  oxygen  absorbed  by  the  combustible  body,  and  ob- 
serve the  proportion  which  the  caloric  bears  to  it. 

Caroline,  But  why  should  the  water,  after  the  combustion  of 
carbon,  rise  in  the  receiver,  since  the  gas  within  it  retains  an 
aeriform  state  ? 

Mrs.  B.  Because  the  carbonic  acid  gas  is  gradually  absorbed 
by  the  water ;  and  this  effect  would  be  promoted  by  shaking 
the  receiver. 

Emily.  The  charcoal  is  now  extinguished,  though  it  is  not 
nearly  consumed ;  it  has  such  an  extraordinary  avidity  for  ox~ 
ygen,  I  suppose,  that  the  receiver  did  not  contain  enough  to  sat- 
isfy the  whole. 

Mrs.  B.  That  is  certainly  the  case ;  for  if  the  combustion 
were  performed  in  the  exact  proportions  of  28  parts  of  carbon 
to  72  of  oxygen,  both  these  ingredients  would  disappear,  and 
100  parts  of  carbonic  acid  would  be  produced. 

Caroline.  Carbonic  acid  must  be  a  very  strong  acid,  since  it 
contains  so  great  a  proportion  of  oxygen  ? 

Mrs.  B.  That  is  a  very  natural  inference  ;  yet  it  is  errone- 
ous. For  the  carbonic  is  the  weakest  of  all  the  acids.  The 
strength  of  an  acid  seems  to  depend  upon  the  nature  of  its  basis, 
and  its  mode  of  combination,  as  well  as  upon  the  proportion  of 
the  acidifying  principle.  The  same  quantity  of  oxygen 
will  convert  some  bodies  into  strong  ackls,  will  01*13  oe  su.u- 
cient  simply  to  oxydate  others. 

Caroline.  Since  this  acid  is  so  weak,  I  think  chemists  should 
have  called  it  the  carbonous,  instead  of  the  carbonic  acid. 

Emily.  But,  I  suppose,  the  carbonous  acid  is  still  weaker, 
and  is  formed  by  burning  carbon  in  atmospherical  air. 

13 


134  CARBON- 

Mrs.  B.  It  has  been  lately  discovered,  that  carbon  may  be 
converted  into  a  gas,  by  uniting  with  a  smaller  proportion  01* 
oxygen  ;  but  as  this  gas  does  not  possess  any  acid  properties, 
it  is  no  more  than  an  oxyd  5  it  is  called  gaseous  oxyd  of  car- 
bon. 

Caroline.  Pray  is  not  carbonic  acid  a  very  wholesome  gas 
to  breathe,  as  it  contains  so  much  oxygen? 

Mrs.  B.  On  the  contrary,  it  is  extremely  pernicious.  Oxy- 
gen, when  in  a  state  of  combination  with  other  substances,  loses, 
in  almost  every  instance,  its  respirable  properties,  and  the  salu- 
brious effects  which  it  has  on  the  animal  economy  when  in  its 
unconfirmed  state.  Carbonic  acid  is  not  only  unfit  for  respira- 
tion, but  extremely  deleterious  if  taken  into  the  lungs. 

Emily.  You  know.  Caroline,  how  very  unwholesome  the 
fumes  of  burning  charcoal  are  reckoned. 

Caroline.  Yes;  but  to  confess  the  truth,  I  did  not  consider 
that  a  charcoal  fire  produced  carbonic  acid  gas. — Can  this  gas 
be  condensed  into  a  liquid  ? 

Mrs.  B.  No  :  for,  as  I  told  you  before,  it  is  a  permanent  elas- 
tic fluid.  But  water  can  absorb  a  certain  quantity  of  this  gas, 
and  can  even  be  impregnated  with  it,  in  a  very  strong  degree, 
by  the  assistance  of  agitation  and  pressure,  as  1  am  going  to 
show  you.  I  shall  decant  some  carbonic  acid  gas  into  this  bot- 
tle, which  I  fill  first  with  water,  in  order  to  exclude  the  atmos- 
pherical air;  the  gas  is  then  introduced  through  ihe  water, 
which  you  see  it  displaces,  for  it  will  not  mix  with  it  in  any 
quantity,  unless  strongly  agitated,  or  allowed  to  stand  over  it 
for  some  time.  The  bottle  is  now  about  half  full  of  carbonic 
acid  gas,  and  the  other  half  is  still  occupied  by  the  water.  By 
corking  the  bottle,  and  then  violently  shaking  it,  in  this  way,  I 
can  mix  the  gas  and  water  together. — INow  will  you  taste  it  ? 

Emily.  It  has  a  distinct  acid  taste. 

Caroline.  Yes,  it  is  sensibly  sour,  and  appears  full  of  little 
bubbles. 

Mrs.  B.  It  possesses  likewise  all  the  other  properties  of  acids, 
but  of  course,  in  a  less  degree  than  the  pure  carbonic  acid  gas. 
as  it  is  so  much  diluted  by  water. 

This  is  a  kind  of  artificial  Seltzer  water.  By  analysing  that 
which  is  produced  by  nature,  it  was  found  to  contain  scarcely 
any  thing  more  than  common  water  impregnated  with  a  certain 
proportion  of  carbonic  acid  gas.  We  are,  therefore,  able  to 
imitate  it,  by  mixing  those  proportions  of  water  and  carbonic 
acid.  Here,  my  dear,  is  an  instance  in  which,  by  a  chemical 
process,  we  can  exactly  copy  the  operations  of  nature  ;  for  the 
artificial  Seltzer  waters  can.  be  made  in  every  respect  similar  t- 


CARBON.  135 

those  of  nature;  in  one  point,  indeed,  the  former  have  an  ad- 
vantage, since  they  may  be  prepared  stronger  or  weaker,  as  oc- 
casion requires. 

Caroline.  I  thought  I  had  tasted  such  water  before.  But 
what  renders  it  so  brisk  and  sparkling  ? 

Mrs.  B.  This  sparkling,  or  effervescence,  as  it  is  called,  is  al- 
ways occasioned  by  the  action  of  an  elastic  fluid  escaping  from 
a  liquid  ;  in  the  artificial  Seltzer  water,  it  is  produced  by  the 
carbonic  acid,  which  being  lighter  than  the  water  in  which  it 
was  strongly  condensed,  flies  off  with  great  rapidity  the  instant 
the  bottle  is  uncorked ;  this  makes  it  necessary  to  drink  it  im- 
mediately. The  bubbling  that  took  place  in  this  bottle  was 
but  trifling,  as  the  water  was  but  very  slightly  impregnated  with 
carbonic  acid.  It  requires  a  particular  apparatus  to  prepare 
the  gaseous  artificial  mineral  waters. 

Emily.  If,  then,  a  bottle  of  Seltzer  water  remains  for  any 
length  of  time  uncorked,  I  suppose  it  returns  to  the  state  of  com- 
mon water  ? 

Mrs.  B.  The  whole  of  the  carbonic  acid  gas,  or  very  nearly 
so,  will  soon  disappear  ;  but  there  is  likewise  in  Seltzer  water  a 
very  small  quantity  of  soda,  and  of  a  few  other  saline  or  earthy 
ingredient,  which  will  remain  in  the  water,  though  it  should  be 
kept  uncorked  for  any  length  of  time. 

Caroline.  I  have  often  heard  of  people  drinking  soda  water. 
Pray  what  sort  of  water  is  that  ? 

Airs.  B.  It  is  a  kind  of  artificial  Seltzer  water,  holding  in  so- 
lution, besides  the  gaseous  acid,  a  particular  saline  substance, 
called  soda,  which  imparts  to  the  water  certain  medicinal  quali- 
ties. 

Caroline.  But  how  can  these  waters  be  so  wholesome,  since 
carbonic  acid  is  so  pernicious  ? 

Mrs.  B.  A  gas,  we  may  conceive,  though  very  prejudical  to 
breathe,  may  be  beneficial  to  the  stomach. — But  it  would  be  of 
no  use  to  attempt  explaining  this  more  fully  at  present. 

Caroline.  Are  waters  never  impregnated  with  other  gases? 

Mrs.  B.  Yes  ;  there  are  several  kinds  of  gaseous  waters.  I 
forgot  to  tell  you  that  waters  have,  for  some  years  past,  been 
prepared,  impregnated  both  with  oxygen  and  hydrogen  gases. 
These  are  not  an  imitation  of  nature,  but  are  altogether  obtain- 
ed by  artificial  means.  They  have  been  lately  used  medicinal- 
ly, particularly  on  the  continent,  where,  I  understand,  they  have 
acquired  some  reputation. 

Emily.  If  I  recollect  right,  Mrs.  B.,  you  told  us  that  carbon 
was  capable  of  decomposing  water  ;  the  affinity  between  oxy- 


136  -CARBON. 

gen  and  carbon  must,  therefore.,  be  greater  than  between  oxy 
gen  and  hydrogen  ? 

Mrs.  B  Yes ;  but  this  is  not  the  case  unless  their  tempera 
Jure  be  raised  to  a  certain  degree.  It  is  only  when  carbon  b 
red-hot,  that  it  is  capable  of  separating  the  oxygen  from  the  hy- 
drogen. Thus,  if  a  small  quantity  of  water  be  thrown  on  a  red- 
hot  fire,  it  will  increase  rather  than  extinguish  the  combustion  , 
for  the  coals  or  wood,  (both  of  which  contain  a  quantity  of  car- 
bon,) decompose  the  water,  and  thus  supply  the  fire  both  with 
oxygen  and  hydrogen  gases.  If,  on  the  contrary,  a  large  mass 
of  water  be  thrown  over  the  fire,  the  diminution  of  heat  thus 
produced  is  such,  that  the  combustible  matter  loses  the  power 
of  decomposing  the  water,  and  the  fire  is  extinguished. 

Emily.  I  have  heard  that  fire-engines  sometimes  do  more 
harm  than  good,  and  that  they  actually  increase  the  fire  when 
they  cannot  throw  water  enough  to  extinguish  it.  It  must  be 
owing,  no  doubt,  to  the  decomposition  of  the  water  by  the  car- 
bon during  the  conflagration. 

Mrs.  B.  Certainly. — The  apparatus  which  you  see  here 
(PLATE  XI.  fig1.  3.),  may  be  used  to  exemplify  what  we  have 
just  said.  It  consists  in  a  kind  of  open  furnace,  through  which 
a  porcelain  tube,  containing  charcoal,  passes.  To  one  end  of 
the  tube  is  adapted  a  glass  retort  with  water  in  it ;  and  the  oth- 
er end  communicates  with  a  receiver  placed  on  the  water-bath. 
A  lamp  being  applied  to  the  retort,  and  the  water  made  to  boil, 
the  vapour  is  gradually  conveyed  through  the  red  hot  charcoal, 
by  which  it  is  decomposed  ;  and  the  hydrogen  gas  which  re- 
sults from  this  decomposition  is  collected  in  the  receiver.  But 
the  hydrogen  thus  obtained  is  far  from  being  pure ;  it  retains  in 
solution  a  minute  portion  of  carbon,  and  contains  also  a  quanti- 
ty of  carbonic  acid.  This  renders  it  heavier  than  pure  hydro- 
•gen  gas,  and  gives  it  some  peculiar  properties  5  it  is  distinguish- 
ed by  the  name  of  carbonated  hydrogen  gas. 

Caroline.  And  whence  does  it  obtain  the  carbonic  acid  that 
is  mixed  with  it  ? 

Emily.  I  believe  I  can  answer  that  question,  Caroline. — 
From  the  union  of  the  oxygen  (proceeding  from  the  decomposed 
water)  with  the  carbon,  which,  you  know,  makes  carbonic  acid. 

Caroline.  True  ;  I  should  have  recollected  that. — The  pro- 
duct of  the  decomposition  of  water  by  red-hot  charcoal,  there- 
fore, is  carbonated  hydrogen  gas,  and  carbonic  acid  gas. 

Mrs.  B,  You  are  perfectly  right  now. 

Carbon  is  frequently  found  combined  with  hydrogen  in  a  state 
of  solidity,  especially  in  coals,  which  owe  their  combusribV 
nature  to  these  two  principles. 


CARBON.  1 37 

Emily.  Is  it  the  hydrogen,  then,  that  produces  the  flame  of 
coals  ? 

Mrs.  B.  It  is  so  ;  and  when  all  the  hydrogen  is  consumed, 
the  carbon  continues  to  burn  without  flame.  But  again,  as  I 
mentioned  when  speaking  of  the  gas-lights,  the  hydrogen  gas 
produced  by  the  burning  of  coals  is  not  pure  :  for,  during  the 
combustion,  particles  of  carbon  are  successively  volatilized 
with  the  hydrogen,  with  which  they  form  what  is  called  a 
hydro  carbonai,  which  is  the  principal  product  of  this  com- 
bustion. 

Carbon  is  a  very  bad  conductor  of  heat ;  for  this  reason,  it 
is  employed  (in  conjunction  with  other  ingredients)  for  coating 
furnaces  and  other  chemical  apparatus. 

Emily.  Pray  what  is  the  use  of  coating  furnaces  ? 

Mrs.  B.  In  most  cases,  in  which  a  furnace  is  used,  it  is  ne- 
cessary to  produce  and  preserve  a  great  degree  of  heat,  for 
which  purpose  every  possible  means  are  used  to  prevent  the 
heat  from  escaping  by  communicating  with  other  bodies,  and 
this  object  is  attained  by  coating  over  the  inside  of  the  furnace 
with  a  kind  of  plaster,  composed  of  materials  that  are  bad 
conductors  of  heat. 

Carbon,  combined  with  a  small  quantity  of  iron,  forms  a 
compound  called  plumbago,  or  black-lead,  of  which  pencils 
are  made.  This  substance,  agreeably  to  the  nomenclature,  is 
a  carburet  of  iron. 

Emily.  Why,  then,  is  it  called  black-lead  ? 

Mrs.  B.  It  is  an  ancient  name  given  to  it  by  ignorant  peo- 
ple, from  its  shining  metallic  appearance  5  but  it  is  certainly  a 
most  improper  name  for  it,  as  there  is  not  a  particle  of  lead  in 
the  composition.  There  is  only  one  mine  of  this  mineral, 
which  is  in  Cumberland.*  It  is  supposed  to  approach  as  near- 
ly to  pure  carbon  as  the  best  prepared  charcoal  does,  as  it  con- 
tains only  five  parts  of  iron,  unadulterated  by  any  other  for- 
eign ingredients.  There  is  another  carburet  of  iron,  in  which 
the  iron,  though  united  only  to  an  extremely  small  proportion 
of  carbon,  acquires  very  remarkable  properties  ;  this  is  steel. 

Caroline.  Really  ;  and  yet  steel  is  much  harder  than  iron  ? 

Mrs.  B.  But  carbon  is  not  ductile  like  iron,  and  therefore 
may  render  the  steel  more  brittle,  and  prevent  its  bending  so 
easily.  Whether  it  is  that  the  carbon,  by  introducing  itself  into 
the  pores  of  the  iron,  and,  by  filling  them,  makes  the  metal 
both  harder  and  heavier ;  or  whether  this  change  depends  up- 

*  She  means  in  England.  Black  lead  is  found  in  a  great  variety  of 
places  in  this  country.  C, 

13* 


138 

on  some  chemical  cause,  I  cannot  pretend  io  decide.  Bn? 
there  is  a  subsequent  operation,  by  which  the  hardness  of  stee? 
is  very  much  increased,  which  simply  consists  in  heating  the 
steel  till  it  is  red-hot,  and  then  plunging  it  into  cold  water. 

Carbon,  besides  the  combination  just  mentioned,  enters  into 
the  composition  of  a  vast  number  of  natural  productions,  such, 
for  instance,  as  all  the  various  kinds  of  oils,  which  result  from 
the  combination  of  carbon,  hydrogen,  and  caloric,  in  various 
proportions. 

Emily.  I  thought  that  carbon,  hydrogen,  and  caloric,  formed 
carbonated  hydrogen  gas  ? 

Mrs.  B.  That  is  the  case  when  a  small  portion  of  carbonic 
acid  gas  is  held  in  solution  by  hydrogen  gas.  Different  propor- 
tions of  the  same  principles,  together  with  the  circumstances  of 
their  union,  produce  very  different  combinations  ;  of  this  you 
will  see  innumerable  examples.  Besides,  we  are  not  now  talk- 
ing of  gases,  but  of  carbon  and  hydrogen,  combined  only  with 
a  quantity  of  caloric,  sufficient  to  bring  them  to  the  consistency 
of  oil  or  fat. 

Caroline.  But  oil  and  fat  are  not  of  the  same  consistence  ? 

Mrs.  B.  Fat  is  only  congealed  oil ;  or  oil,  melted  fat.  The 
-one  requires  a  little  more  heat  to  maintain  it  in  a  fluid  state  than 
the  other.  Have  you  never  observed  the  fat  of  meat  turned  to 
oil  by  the  caloiic  it  has  imbibed  from  the  fire  ? 

Emily.  Yet  oils  in  general,  as  salad-oil,  and  lamp-oil,  do  not 
turn  to  fat  when  cold  ? 

Mrs.  B.  JNot  at  the  common  temperature  of  the  atmosphere, 
because  they  retain  too  much  caloric  to  congeal  at  that  tem- 
perature ;  but  if  exposed  to  a  sufficient  degree  of  cold,  their 
latent  heat  is  extricated,  and  th«y  become  solid  fat  substances* 
Have  you  never  seen  salad-oil  frozen  in  winter  ? 

Emily.  Yes  ;  but  it  appears  to  me  in  that  state  very  differ- 
ent from  animal  fat. 

j\irs.  B.  The  essential  constituent  parts  of  either  vegetable 
or  animal  oils  are  the  same,  carbon  and  hydrogen  ;  their  vari- 
ety arises  from  the  different  proportions  of  these  substances, 
and  from  other  accessory  ingredients  that  may  be  mixed  with 
them.  The  oil  of  a  whale,  and  the  oil  of  roses,  are,  in  their  es- 
sential constituent  parts,  the  same ;  but  the  one  is  impregnated 
with  the  offensive  particles  of  animal  matter,  the  other  with  the 
delicate  perfume  of  a  flower. 

The  difference  of  Jixed  oils,  and  volatile  or  essential  oils, 
consists  also  in  the  various  proportions  of  carbon  and  hydro- 
gen. Fixed  oils  are  those  which  will  not  evaporate  without 
being  decomposed ;  this  is  the  case  with  all  common  oils,  which 


CARBON,  189 

contain  a  greater  proportion  of  carbon  than  the  essential  oils. 
The  essential  oils  (which  comprehend  the  whole  class  of  essen- 
ces and  perfumes)  are  lighter  5  they  contain  more  equal  propor- 
tions of  carbon  and  hydrogen,  and  are  volatilized  or  evapora- 
ted without  being  decomposed. 

Emily.  When  you  say  that  one  kind  of  oil  will  evaporate^ 
and  the  other  be  decomposed,  you  mean,  I  suppose,  by  the 
application  of  heat  ? 

Mrs.  B.  Not  necessarily  ;  for  there  are  oils  that  will  evapo- 
rate slowly  at  the  common  temperature  of  the  atmosphere  ; 
but  for  a  more  rapid  volatilization,  or  for  their  decomposition; 
the  assistance  of  heat  is  required.* 

Caroline.  I  shall  now  remember,  I  think,  that  fat  and  oil  are 
really  the  same  substances,  both  consisting  of  carbon  and  hy- 
drogen ;  that  in  fixed  oils  the  carbon  preponderates,  and  "heat 
produces  a  decomposition  ;  while,  in  essential  oils,  the  propor- 
tion of  hydrogen  is  greater,  and  heat  produces  a  volatilization 
only. 

Emily.  I  suppose  the  reason  why  oil  burns  so  well  in  lamps 
is  because  its  two  constituents  are  so  combustible  ? 

Mrs.  B.  Certainly  ;  the  combustion  of  oil  is  just  the  same 
as  that  of  a  candle  ;  if  tallow,  it  is  only  oil  in  a  concrete  state  ; 
if  wax,  or  spermaceti,  its  chief  chemical  ingredients  are  still 
hydrogen  and  carbon, 

Emily.  I  wonder,  then,  there  should  be  so  great  a  difference 
between  tallow  and  wax  ? 

Mrs.  B.  I  must  again  repeat,  that  the  same  substances,  in 
different  proportions,  produce  results  that  have  sometimes 
scarcely  any  resemblance  to  each  other.  Bat  this  is  rather  a 
general  remark  that  I  wish  to  impress  upon  your  minds,  than 
one  which  is  applicable  to  the  present  case  ;  for  tallow  and  wax 
are  far  from  being  very  dissimilar  ;  the  chief  difference  con- 
sists in  the  wax  being  a  purer  compound  of  carbon  and  hydro- 
gen than  the  tallow,  which  retains  more  of  the  gross  particles 
®f  animal  matter.  The  combustion  of  a  candle,  and  that  of 
a  lamp,  both  produce  water  and  carbonic  acid  gas.  Can  you 
tell  me  how  these  are  formed  ? 

Emily.  Let  me  reflect ....  Both  the  candle  and  lamp  burn 
by  means  of  fixed  oil — this  is  decomposed  as  the  combustion 

*  The  volatile  or  essential  oils  evaporate  when  exposed  to  the  air. 
Hence  the  odor  which  oil  01  lavender,  peppermint,  £c.  give  out.  The 
animal  oils,  and  what  are  called  expressed  oils,  as  that  of  castor,  £c. 
do  not  evaporate.  Hence  a  good  test  of  the  purity  of  essential  oil, 
is,  to  let  a  drop  fall  on  paper.  If  a  grease-spot  remains  after  a  few 
minutes,  it  is  adulterated  with  some  fixed  oil,  C. 


140  CARBONS 

goes  on  ;  and  the  constituent  parts  of  the  oil  being  thus  sepa- 
rated, the  carbon  unites  with  a  portion  of  oxygen  from  the  at- 
mosphere to  form  carbonic  acid  gas,  whilst  the  hydrogen  com- 
bines with  another  portion  of  oxygen,  and  forms  with  it  water. 
The  products,  therefore,  of  the  combustion  of  oils  are  water  and 
carbonic  acid  gas 

Caroline.  But  we  see  neither  water  nor  carbonic  acid  pro- 
duced by  the  combustion  of  a  candle. 

Mrs.  B.  The  carbonic  acid  gas,  you  know,  is  invisible,  and 
the  water  being  in  a  state  of  vapour,  is  so  likewise.  E roily  is 
perfectly  correct  in  her  explanation,  and  I  am  very  much  plea- 
sed with  it. 

All  the  vegetable  acids  consist  of  various  proportions  of  car- 
bon and  hydrogen,  acidified  by  oxygen.  Gums,  sugar,  and 
starch,  are  likewise  composed  of  these  ingredients  ;  but,  as  the 
oxygen  which  they  contain  is  not  sufficient  to  convert  them  into 
acids,  they  are  classed  with  the  oxyds,  and  called  vegetable 
oxyds. 

Caroline.  I  am  very  much  delighted  with  all  these  new  ideas ; 
but,  at  the  same  time,  1  cannot  help  being  apprehensive  that 
I  may  forget  many  of  them. 

Mrs.  B.  I  would  advise  you  to  take  notes,  or,  what  would 
answer  better  still,  to  write  down,  after  every  lesson,  as  much 
of  it  as  you  can  recollect.  And,  in  order  to  give  you  a  little 
assistance,  I  shall  lend  you  the  heads  or  index,  which  I  occa* 
sionally  consult  for  the  sake  of  preserving  some  method  and 
arrangement  in  these  conversations.  Unless  you  follow  some 
such  plan,  you  cannot  expect  to  retain  nearly  all  that  you  learn, 
how  great  soever  be  the  impression  it  may  make  on  you  at  first. 

Emily.  I  will  certainly  follow  your  advice. — Hitherto  I  have 
found  that  I  recollected  pretty  well  what  you  have  taught  us  ; 
but  the  history  of  carbon  is  a  more  extensive  subject  than  any 
of  the  simple  bodies  we  have  yet  examined. 

Mrs.  />'.  I  have  little  more  to  say  on  carbon  at  present;  but 
hereafter  you  will  see  that  it  performs  a  considerable  part  in 
most  chemical  operations. 

Caroline.  That  is,  I  suppose,  owing  to  its  entering  into  the 
composition  of  so  sfreat  a  variety  of  substances  ? 

*i/r«.  ".  Certainly  ;  it  is  the  basis,  you  have  seen,  of  all  veg- 
etable matter ;  and  you  will  find  that  it  is  very  essential  to  the 
process  of  animalization.  But  in  the  mineral  kingdom  also, 
particularly  in  its  form  of  carbonic  acid,  we  shall  often  discov- 
er it  combined  with  a  great  .variety  of  substances. 

In  chemical  operations,  carbon  is  particularly  useful,  from 
its  very  great  attraction  for  oxygen,  as  it  will  absorb  this  sub- 


MET.VLS.  141 

stance  i'rom  many  oxygenated  or  burnt  bodies,  and  thus  deoxy- 
genate,  or  unburn  them,  and  restoie  them  to  their  original  com- 
bustible state. 

Caroline.  I  do  not  understand  how  a  body  can  be  unburnt* 
and  restored  to  its  original  state.  This  piece  of  tinder,  for  in- 
stance, that  has  been  burnt,  if  by  any  means  the  oxygen  were 
extracted  from  it,  would  not  be  restored  to  its  former  state  of 
linen  ;  for  its  texture  is  destroyed  by  burning,  and  that  must  be 
the  case  with  all  organized  or  manufactured  substances,  as  you 
observed  in  a  former  conversation. 

Mrs.  B.  A  compound  body  is  decomposed  by  combustion  in 
a  way  which  generally  precludes  the  possibility  of  restoring  it 
to  its  former  state;  the  oxygen,  for  instance,  does  not  become 
fixed  in  the  tinder,  but  it  combines  with  its  volatile  parts,  and 
flies  off  in  the  shape  of  gas,  or  watery  vapour.  You  see, 
therefore,  how  vain  it  would  be  to  attempt  the  recomposition  of 
such  bodies.  But,  with  regard  to  simple  bodies,  or  at  least  bod- 
ies whose  component  parts  are  not  distributed  by  the  process  of 
oxygenation  or  .deoxygenation,  it  is  often  possible  to  restore 
them,  after  combustion,  to  their  original  state. — The  metals, 
for  instance,  undergo  no  other  alteration  by  combustion  than  a 
combination  with  oxygen  ;  therefore,  when  the  oxygen  is  taken 
from  them,  they  return  to  their  pure  metallic  state.  But!  shall 
say  nothing  further  of  this  at  present,  as  the  metals  will  furnish 
ample  subject  for  another  morning ;  and  they  are  the  class  ol 
simple  bodies  that  come  next  under  consideration. 


CONVERSATION  X, 

ON  METALS. 

Mrs.  B.  THE  METALS,  which  we  are  now  to  examine,  are 
bodies  of  a  very  different  nature  from  those  which  we  have 
hitherto  considered.  They  do  not,  like  the  bases  of  gases, 
elude  the  immediate  observation  of  our  senses ;  for  they  are 
the  most  brilliant,  the  most  ponderous,  and  the  most  palpable 
substances  in  nature. 

Caroline.  I  doubt,  however,  whether  the  metals  will  appear 
to  us  so  interesting,  and  give  us  so  much  entertainment  as  those 
mysterious  elements  which  conceal  themselves  from  our  view. 
Besides,  they  cannot  afford  so  much  novelty ;  they  are  bodies 
with  which  we  are  already  so  well  acquainted. 

Airs.  B.  You  are  not  aware,  my  dear,  of  the  interesting  dis 


142  METALS. 

coveries  which  were  a  few  years  ago  made  by  Sir  H.  Davy  re- 
specting this  class  of  bodies.  By  the  aid  of  the  Voltaic  batte- 
ry, he  has  obtained  from  a  variety  of  substances,  metals  before 
unknown,  the  properties  of  which  are  equally  new  aud  curious. 
We  shall  begin,  however,  by  noticing  those  metals  with  which 
you  profess  to  be  so  well  acquainted.  But  the  acquaintance, 
you  will  soon  perceive,  is  but  very  superficial  5  and  1  trust  that 
you  will  find  both  novelty  and  entertainment  in  considering 
the  metals  in  a  chemical  point  of  view.  To  treat  of  this  sub- 
ject fully,  would  require  a  whole  course  of  lectures ;  for  metals 
form  of  themselves  a  most  important  branch  of  practical  chem- 
istry. We  must,  therefore,  confine  ourselves  to  a  general  view 
of  them.  These  bodies  are  seldom  found  naturally  in  their 
metallic  form  ;  they  are  generally  more  or  less  oxygenated  or 
combined  with  sulphur,  earths,  or  acids,  and  are  often  blended 
with  each  other.  They  are  found  buried  in  the  bowels  of  the 
earth  in  most  parts  of  the  world,  but  chiefly  in  mountainous 
districts,  where  the  surface  of  the  globe  has  been  disturbed  by 
earthquakes,  volcanoes,  and  other  convulsions  of  nature.  They 
are  spread  in  strata  or  beds,  called  veins,  and  these  veins  are 
composed  of  a  certain  quantity  of  metal,  combined  with  vari- 
ous earthy  substances,  with  which  they  form  minerals  of  dif- 
ferent nature  and  appearance,  which  are  called  ores. 

Caroline.  I  now  feel  quite  at  home,  for  my  father  has  a 
lead- mine  in  Yorkshire,  and  I  have  heard  a  great  deal  about 
veins  of  ore,  and  of  the  roasting  and  smelting  of  the  lead ; 
but,  I  confess,  that  I  do  not  understand  in  what  these  operations 
consist. 

Mrs.  B.  Roasting  is  the  process  by  which  the  volatile  parts 
of  the  ore  are  evaporated  ;  smelting,  that  by  which  the  pure 
metal  is  afterwards  separated  from  the  earthy  remains  of  the 
ore.  This  is  done  by  throwing  the  whole  into  a  furnace,  and 
mixing  with  it  certain  substances  that  will  combine  with  the 
earthy  parts  and  other  foreign  ingredients  of  the  ore;  the  met- 
al being  the  heaviest,  falls  to  the  bottom,  and  runs  out  by  prop- 
er openings  in  its  pure  metallic  state. 

Emily.  You  told  us  in  a  preceding  lesson  that  metals  had  a 
great  affinity  for  oxygen.  Do  they  not,  therefore,  combine 
with  oxygen,  when  strongly  heated  in  the  furnace,  and  run  out 
in  the  state  of  oxyds  ? 

Mrs.  K.  No  ;  for  the  scoriae,  or  oxyd,  which  soon  forms  on 
the  surface  of  the  fused  metal,  when  it  is  oxydable,  prevents 
the  air  from  having  any  farther  influence  on  the  mass  j  so  that 
neither  combustion  nor  oxygenation  can  take  place. 

Caroline.  Are  all  the  metals  equally  combustible  ? 


METALS.  143 

Mrs.  B.  No ;  their  attraction  for  oxygen  varies  extremely. 
There  are  some  that  will  combine  with  it  only  at  a  very  high 
temperature,  or  by  the  assistance  of  acids  ;  whilst  there  are,, 
others  that  oxydate  spontaneously  and  with  great  rapidity,  even 
at  the  lowest  temperature  5  such  is  in  particular  manganese, 
which  scarcely  ever  exists  in  the  metallic  state,  as  it  immedi- 
ately absorbs  oxygen  on  being  exposed  to  the  air,  and  crumbles 
to  an  oxyd  in  the  course  of  a  few  hours. 

Emily.  Is  not  that  the  oxyd  from  which  you  extracted  the 
oxygen  gas  ? 

Airs.  B.  It  is  :  so  that,  you  see,  this  metal  attracts  oxygen  at 
a  low  temperature,  and  parts  with  it  when  strongly  heated. 

Emily.  Is  there  any  other  metal  that  oxydates  at  the  temper- 
ature of  the  atmosphere  ? 

Mrs.  B.  They  all  do,  more  or  less,  excepting  gold,  silver, 
and  platina. 

Copper,  lead,  and  iron,  oxydate  slowly  in  the  air,  and  cover 
themselves  with  a  sort  of  rust,  a  process  which  depends  on  the 
gradual  conversion  of  the  surface  into  an  oxyd.  This  rusty 
surface  preserves  the  interior  metal  from  oxydation,  as  it  pre- 
vents the  air  from  coming  in  contact  with  it.  Strictly  speaking, 
however,  the  word  rust  applies  only  to  the  oxyd,  which  forms 
on  the  surface  of  iron,  when  exposed  to  air  and  moisture, 
which  oxyd  appears  to  be  united  with  a  small  portion  of  car- 
bonic acid. 

Emily.  When  metals  oxydate  from  the  atmosphere  without 
an  elevation  of  temperature,  some  light  and  heat,  I  suppose, 
must  be  disengaged,  though  not  in  sufficient  quantities  to  be 
sensible. 

Mrs.  B.  Undoubtedly  ;  and,  indeed,  it  is  not  surprising  that 
in  this  case  the  light  and  heat  should  not  be  sensible,  when  you 
consider  how  extremely  slow,  and,  indeed,  how  imperfectly, 
most  metals  oxydate  by  mere  exposure  to  the  atmosphere.  For 
the  quantity  of  oxygen  with  which  metals  are  capable  of  com- 
bining, generally  depends  upon  their  temperature ;  and  the 
absorption  stops  at  various  points  of  oxydation,  according  to 
the  degree  to  which  their  temperature  is  raised. 

Emily.  That  seems  very  natural  ;  for  the  greater  the  quan- 
tity of  caloric  introduced  into  a  metal,  the  more  will  its  positive 
electricity  be  exalted,  and  consequently  the  stronger  will  be 
its  affinity  for  oxygen. 

Mrs.  B.  Certainly.  When  the  metal  oxygenates  with  suf- 
ficient rapidity  for  light  and  heat  to  become  sensible,  combus- 
tion actually  takes  place.  But  this  happens  only  at  very  high 
temperatures,  and  the  product  is  nevertheless  an  oxyd ;  for 


t44  METALS. 

though,  as  I  have  just  said,  metals  will  combine  with  different 
proportions  of  oxygen,  yet  with  the  exception  of  only  five  of 
^hem,  they  are  not  susceptible  of  acidification. 

Metals  change  colour  during  the  different  degrees  of  oxyda- 
tion  which  they  undergo.  Lead,  when  heated  in  contact  with 
the  atmosphere,  first  becomes  grey  ;  if  its  temperature  be  then 
raised;  it  turns  yellow,  and  a  still  stronger  heat  changes  it  to 
red.  Iron  becomes  successively  a  green,  brown,  and  white 
oxyd.  Copper  changes  from  brown  to  blue,  and  lastly  green. 

Emily.  Pray,  is  the  white  lead  with  which  houses  are  pain- 
ted prepared  by  oxydating  lead  ? 

Mrs.  B.  Not  merely  by  oxydating,  but  by  being  also  united 
with  carbonic  acid.  It  is  a  carbonat  of  lead.  The  mere  oxyd 
of  lead  is  called  red  lead.  Litharge  is  another  oxyd  of  lead, 
containing  less  oxygen.  Almost  all  the  metallic  oxyds  are  used 
as  paints.  The  various  sorts  of  ochres  consist  chiefly  of  iron 
more  or  less  oxydated.  And  it  is  a  remarkable  circumstance, 
that  if  you  burn  metals  rapidly,  the  light  or  flame  they  emit  du- 
ring combustion  partakes  of  the  colours  which  the  oxyd  succes- 
sively assumes. 

Caroline.  How  is  that  accounted  for,  Mrs.  B.,  since  light 
does  not  proceed  from  the  burning  body,  but  from  the  decom- 
position of  the  oxygen  gas  ? 

Mrs.  B.  The  correspondence  of  the  colour  of  the  light  with 
that  of  the  oxyd  which  emits  it,  is,  in  all  probability,  owing  to 
some  particles  of  the  metal  which  are  volatilised  and  carried  off 
by  the  caloric. 

Caroline.  It  is  then  a  sort  of  metallic  gas. 

Why  is  it  reckoned  so  unwholsome  to  breathe  the  uir  of  a 
place  in  which  metals  are  melting  ? 

Mrs.  B.  Perhaps  the  notion  is  too  generally  entertained* 
But  it  is  true  with  respect  to  lead,  and  some  other  noxious  met- 
als, because,  unless  care  be  taken,  the  particles  of  the  ox- 
yd which  are  volatilized  by  the  heat,  are  inhaled  in  with  the 
breath,  and  may  produce  dangerous  effects. 

I  must  show  you  some  instances  of  the  combustion  of  metals ; 
it  would  require  the  heat  of  a  furnace  to  make  them  burn  in 
the  common  air,  but  if  we  supply  them  with  a  stream  of  oxy- 
gen gas,  we  may  easily  accomplish  it. 

Caroline.  But  it  will  still,  I  suppose,  be  necessary  in  some 
degree  to  raise  their  temperature  ? 

Mrs.  B.  This,  as  you  shall  see,  is  very  easily  done,  particu- 
larly if  the  experiment  be  tried  upon  a  small  scale. — I  begin  by 
lighting  this  piece  of  charcoal  with  the  candle,  and  then  in- 


Fig  1  fimi'tiry  charfoaZ  with  a  tatper  IC&ka-jfjjpc.   Flff.  2.  Combustion  of mf  faff 
by  fnfatif  or  a  &/CW-THIX  conveying  a  strftutt  of"  oxygen  gra-f  from  a 


METALS.  145 

crease  the  r^idity  of  its  combustion  by  blowing  upon  it  with  a 
blow-pipe.  (PLATE  XII.  fig.  1.) 

Emily.  That  I  do  not  understand  ;  for  it  is  not  every  kind  of 
air,  but  merely  oxygen  gas,  that  produces  combustion.  Now 
you  said  that  in  breathing  we  inspired,  but  did  not  expire 
oxygen  gas.  Why,  therefore,  should  the  air  which  you 
breathe  through  the  blow-pipe  promote  the  combustion  of  the 
charcoal  ? 

Mrs.  B.  Because  the  air,  which  has  but  once  passed  through 
the  lungs,  is  yet  but  little  altered,  a  small  portion  only  of  its 
oxygen  being  destroyed  ;  so  that  a  great  deal  more  is  gained  by 
ncreasing  the  rapidity  of  the  current,  by  means  of  the  blow- 
pipe, than  is  lost  in  consequence  of  the  airj^ssing  once  through 
the  lungs,  as  you  shall  see  —  '* 

Emily.  Yes,  indeed,  it  makes  the  charcoal  burn  much 
brighter. 

Mrs.  B.  Whilst  it  is  red-hot,  I  shall  drop  some  iron  filings 
on  it,  and  supply  them  with  a  cm  rent  of  oxygen  gi.*,  by  means 
of  this  apparatus,  (PLATE  XII.  fig.  2.)  which  consists  simply 
of  a  closed  tin  cylindrical  vessel,  full  of  oxygen  gas,  with  two 
apertures  and  stop-cocks,  by  one  of  which  a  stream  of  water  is 
thrown  into  the  vessel  through  a  long  funnel,  whilst  by  the 
other  the  gas  is  forced  out  through  a  blow-pipe  adapted  to  it,  as 
the  water  gains  admittance. — I\ow  that  I  pour  water  into  the 
funnel,  you  may  hear  the  gas  issuing  from  the  blow-pipe — I 
bring  the  charcoal  close  to  the  current,  and  drop  the  filings  up*- 
on  it  — 

Caroline.  They  emit  much  the  same  vivid  light  as  the  com- 
bustion of  the  iron  wire  in  oxygen  gas. 

Mrs.  B.  The  process  is,  in  fact,  the  same;  there  is  only  some 
difference  in  the  mode  of  conducting  it.  Let  us  burn  some  tin 
in  the  same  manner — you  see  that  it  is  equally  combustible. — • 
Let  us  now  try  some  copper — 

Caroline.  This  burns  with  a  greenish  flame  ;  it  is,  I  suppose, 
owing  to  the  colour  of  the  oxyd  ? 

Emily.  Pray,  shall  we  not  also  burn  some  gold  ? 

Mrs.  #.  That  is  not  in  our  power,  at  least  in  this  way. — - 
Gold,  Silver,  and  platina,  are  incapable  of  being  oxydated  by 
the  greatest  heat  that  we  can  produce  by  the  common  method. 
It  is  from  this  circumstance,  that  they  have  been  called  perfect 
metals.  Even  these,  however,  have  an  affinity  for  oxygen  ; 
but  their  oxydation  or  combustion  can  be  performed  only  by 
me.ans  of  acids  or  by  electricity. 

The  spark  given  out  by  the  Voltaic  battery  produces  at  the 
point  of  contact  a  greater  degree  of  heat  than  any  other  pre- 
14 


146  METALS. 

cess  ;  and  it  is  at  this  very  high  temperature  onl^hat  the  af- 
finity of  these  metals  for  oxygen  will  enable  them  to  act  on  each 
other.  • 

I  am  sorry  that  I  cannot  show  you  the  combustion  of  the 
perfect  metals  by  this  process,  but  it  requires  a  considerable 
Voltaic  battery.  You  will  see  these  experiments  performed  in 
the  most  perfect  mariner,  when  you  attend  the  chemical  lec- 
tures of  the  Royal  Institution.  But  in  the  mean  time  I  can, 
without  difficulty,  show  you  an  ingenious  apparatus  lately  con- 
trived tor  the  purpose  of  producing  intense  heats,  the  power  of 
which  nearly  equals  that  of  the  largest  Voltaic  batteries.  It 
simply  consists,  you  see,  in  a  strong  box,  made  of  iron  or  cop- 
per, PLATE  X  iig.^^)  to  which  may  be  adapted  this  air-syringe 
or  condensing-pum^P^md  a  stop-cock  terminating  in  a  small 
orifice  similar  to  that  of  a  blow-pipe.  By  working  the  conden- 
sing syringe,  up  and  down  in  this  manner,  a  quantity  of  air  is 
accumulated  in  the  vessel,  which  may  be  increased  to  almost 
any  extent  t  so  that  if  we  now  turn  the  stop-cock,  the  conden- 
sed air  will  rush  out,  forming  a  jet  of  considerable  force  ;  and 
if  we  place  the  flame  of  a  lamp  in  the  current,  you  will  see  how 
violently  the  flame  is  driven  in  that  direction. 

Caroline.  It  seems  to  be  exactly  the  same  effect  as  that  of 
a  blow-pipe  worked  by  the  mouth,  only  much  stronger. 

Emily.  \es  ;  and  this  new  instrument  has  this  additional  ad- 
vantage, that  it  does  not  fatigue  the  mouth  and  lungs  like  the 
common  blow-pipe,  and  requires  no  art  in  blowing. 

Mrs.  B.  Unquestionably  ;  but  yet  this  blow-pipe  would  be 
of  very  limited  utility,  if  its  energy  and  power  could  not  be 
greatly  increased  by  some  other  contrivance.  Can  you  imagine 
any  mode  of  producing  such  an  effect  ? 

Emily.  Could  not  the  reservoir  b'e  charged  with  pure  oxy- 
gen, instead  of  common  air,  as  in  the  case  of  the  gas-holder  ? 

Mrs.  B.  Undoubtedly  ;  and  this  is  precisely  the  contrivance 
I  allude  to.  The  vessel  need  only  be  supplied  with  air  from  a 
bladder  full  of  oxygen,  instead  of  the  air  of  the  room,  and 
this,  you  see,  may  be  easily  ^one  by  screwing  the  bladder  on 
the  upper  part  of  the  syringe,  so  that  in  working  the  syringe  the 
oxygen  gas  is  forced  from  the  bladder  into  the  condensing  ves- 
sel. 

Caroline.  With  the  aid  of  this  small  apparatus,  therefore, 
we  could  obtain  the  same  effects  as  those  we  have  just  produced 
with  the  gas-holder,  by  means  of  a  column  of  water  forcing  the 
gas  out  of  it  ? 

Mrs.  B.  Yes  ;  and  much  more  conveniently  so.  But  therr 
is  a  mode  of  using  this  apparatus  by  which  more  powerful  ef- 


METALS.  147 

fects  still  may  be  obtained.  It  consists  in  condensing  in  the 
reservoir,  not  oxygen  alone,  but  a  mixture  of  oxygen  and  hy- 
itvjen  in  the  exact  proportion  in  which  they  unite  to  produce 
water ;  and  then  kindling  the  jet  formed  by  the  mixed  gases. 
The  heat  disengaged  by  this  combustion,  without  the  help  of 
my  lamp,  is  probably  the  most  intense  of  any  known;  and  va- 
rious effects  are  said  to  have  been  obtained  from  it  which  ex- 
ceed all  expectation. 

Caroline.  But  why  should  we  not  try  this  experiment  ? 

Mrs.  B.  Because  it  is  not  exempt  from  danger  5*  the  com* 
bustion  (notwitstanding  various  contrivances  which  have  been 
resorted  to  with  a  view  to  prevent  accident)  being  apt  to  pene- 
trate into  the  inside  of  the  vessel,  and  to  produce  a  dangerous 
and  violent  explosion.  We  shall,  therefore,  now  proceed  in  our 
subject. 

Caroline.  I  think  you  said  the  oxyds  of  metals  could  be  re- 
stored to  their  metallic  state  ? 

Mrs.  B.  Yes  ;  this  is  called  reviving  a  metal.  Metals  are 
in  general  capable  of  being  revived  by  charcoal,  when  heated 
red  hot,  charcoal  having  a  greater  attraction  lor  oxygen  than 
the  metals.  You  need  only,  therefore,  decompose,  or  unburn 
the  oxyd,  by  depriving  it  of  its  oxygen,  and  the  metal  will  be 
restored  to  its  pure  state. 

Emily.  But  will  the  carbon,  by  this  operation,  be  burnt,  and 
be  converted  into  carbonic  acid  ? 

Mrs.  B.  Certainly.  There  are  other  combustible  substances 
to  which  metals  at  a  high  temperature  will  part  with  their  oxy- 
gen. They  will  also  yield  it  to  each  other,  according  to  their 
several  degrees  cf  attraction  for  it ;  and  if  the  oxygen  goes'  i"t" 
a  more  dense  state  in  the  metal  which  it  enters,  than  it  existed 
in  that  in  which  it  quits,  a  proportional  disengagement  of  calo- 
ric will  take  place. 

Caroline.  And  cannot  the  oxyds  of  gold,  silver,  and  platina, 
which  are  formed  by  means  of  acids  or  of  the  electric  fluid,  be 
restored  to  iheir  metallic  state  ? 

Mrs.  B.  Yes,  they  may  ;  and  the  intervention  of  a  combust- 

*  Hydrogen  and  oxygon  may  be  burned  together  with  the  most  per- 
fect safety  by  means  of  the  compound  blow-pipe,  an  instrument  invent- 
ed by  Prof.  Hare,  of  Philadelphia.  Instead  of  mixing  the  gases  in  the 
L^ame  reservoir,  they  are  kept  separate  until  they  meet  at  the  point  of 
combustion.  An  account  of  this  blow-pipe  is  given  by  Prof.  Sillitnan, 
in  his  edition  of  Henry's  chemistry,  together  with  a  list  of  experi- 
ments made  with  it  on  various  substances.  This  was  the  first  notice 
of  any  experiment  made  by  burning  the  two  gases  together,  for  the 
;>vrpose  of  obtaining  an  intense  heat,  C, 


148  METALS. 

able  body  is  not  required  ;  heat  alone  will  take  the  oxygen  front 
them,  convert  it  into  a  gas,  and  revive  the  metal.  ' 

Emily.  You  said  that  rust  was  an  oxyd  of  iron  ;  how  is  it^ 
then,  that  water,  or  merely  dampness,  produces  it,  which,  you 
know,  it  very  frequently  does  on  steel  grates,  or  any  iron  in- 
struments ? 

Mrs.  B.  In  that  rase  the  metal  decomposes  the  wa\ter,  or 
dampness  (which  is  nothing  but  water  in  a  state  of  vapour),  and 
obtains  the  oxygen  from  it. 

Caroline.  I  thought  that  it  was  necessary  to  bring  metals-  to 
;i  very  high  temperature  to  enable  them  to  decomposed  water. 

Mrs.  B.  It  is  so,  if  it  required  that  the  process  should  be 
performed  rapidly,  and  if  any  considerable  quantity  is  to  be 
decomposed.  Rust,  you  know,  is  sometimes  months  in  form- 
ing, and  then  it  is  only  the  surface  of  the  metal  that  is  oxyda- 
ted. 

Emily.  Metals,  then,  that  do  not  rust,  are  incapable  of  spon- 
taneous oxydation,  either  by  air  or  water  ? 

Mrs.  B.  Yes  ;  and  this  is  th£  case  with  the  perfect  metals; 
which,  on  that  account,  preserve  their  metallic  lustre  so  well. 

Emily.  Are  all  metals  capable  of  decomposing  water,  pro- 
vided their  temperature  be  sufficiently  raised  ? 

Mrs.  B.  No  ;  a  certain  degree  of  attraction  is  requisite,  be- 
sides the  assistance  of  heat.  Water,  you  recollect,  is  compo- 
sed of  oxygen  and  hydrogen ;  and,  unless  the  affinity  of  the 
metal  for  oxygen  be  stronger  than  that  of  hydrogen,  it  is  in  vain 
that  we  raise  its  temperature,  for  it  cannot  take  the  oxygen 
from  the  hydrogen.  Iron,  zinc,  tin,  and  antimony,  have  a 
stronger  affinity  for  oxygen  than  hydrogen  has,  therefore  these 
four  metals  are  capable  of  decomposing  water.  But  hydrogen 
having  an  advantage  over  all  the  other  metals  with  respect  to 
its  affinity  for  oxygen,  it  not  only  withholds  its  oxygen  from 
them,  but  is  even  capable,  under  certain  circumstances,  of  ta- 
king the  oxygen  from  the  oxyds  of  these  metals. 

Emily.  I  confess  that  I  do  not  quite  understand  why  hydro- 
gen can  take  oxygen  from  those  metals  that  do  not  decompose 
water. 

Caroline.  Now  I  think,  I  do  perfectly.  Lead,  for  instance? 
will  not  decompose  water,  because  it  has  not  so  strong  an  at- 
traction for  oxygen  as  hydrogen  has.  Well,  then,  suppose  .the 
lead  to  be  in  a'state  of  oxyd ;  hydrogen  will  take  the  oxygen 
from  the  lead,  and  unite  with  it  to  form  water,  because  hydro- 
gen has  a  stronger  attraction  for  oxygen,  than  oxygen  has  for 
iead  ;  and  it  is  the  same  with  all  the  other  metals  which  do  no? 
decompose  water, 


METALS.  149 

B tnily.  \  understand  your  explanation,  Caroline,  very  well ; 
and  I  imagine  that  it  is  because  lead  cannot  decompose  water 
that  it  is  so  much  employed  for  pipes  for  conveying  that  fluid.* 

J\lrs.  B .  Certainly ;  lead  is,  on  that  account,  particularly 
appropriate  to  such  purposes ;  whilst,  on  the  contrary,  this 
metal,  if  it  was  oxydable  by  water,  would  impart  to  it  very 
noxious  qualities,  as  all  oxyds  of  lead  are  more  or  less  perni- 
cious. 

But,  with  regard  to  the  oxydation  of  metals,  the  most  pow- 
erful mode  of  effecting  it  is  by  means  of  acids.  These,  you 
know,  contain  a  much  greater  proportion  of  oxygen  than  either 
air  or  water;  and  will,  most  of  them,  easily  yield  it  to  metals. 
Thus,  you  recollect,  the  zinc  plates  of  the  Voltaic  battery  are 
oxydated  by  the  acid  and  water,  much  more  effectually  than  by 
water  alone. 

Caroline.  And  I  have  often  observed  that  if  I  drop  vinegar, 
lemon,  or  any  acid  on  the  blade  of  a  knife,  or  on  a  pair  of  scis- 
sors, it  will  immediately  produce  a  spot  of  rust. 

Emily.  Metals  have,  then,  three  ways  of  obtaining  oxygen  ; 
from  the  atmosphere,  from  water,  and  from  acids. 

Mrs.  B.  The  two  first  you  have  already  witnessed,  and  I 
shall  now  show  you  how  metals  take  the  oxygen  from  an  arid. 
This  bottle  contains  nitric  acid  ;  I  shall  pour  some  of  it  over 
this  piece  of  copper-leaf. 

Caroline.  Oh,  what  a  disagreeable  smell  ! 

Emily.  And  what  is  it  that  produces  the  effervescence  anc 
that  thick  yellow  vapour  ? 

Mrs.  B.  It  is  the  acid,  which  being  abandoned  by  the  great- 
est part  of  its  oxygen,  is  converted  into  a  weaker  acid,  which 
escapes  in  the  form  of  gas. 

Caroline.  And  whence  proceeds  this  heat  ? 

Mrs.  B.  Indeed,  Caroline,  I  think  you  might  now  be  able  te 
answer  that  question  yourself. 

Caroline.  Perhaps  it  is  that  the  oxygen  enters  into  the  metal 
in  a  more  solid  state  than  it  existed  in  the  acid,  in  consequence 
of  which  caloric  is  disengaged. 

Airs.  B.  If  the  combination  of  the  oxygen  and  the  metal  re- 
sults from  the  union  of  their  opposite  electricities,  of  course 
caloric  must  be  given  out. 

Emily.  The  effervescence  is  over;  therefore  I  suppose  that 
the  metal  is  now  oxydated. 

*  Lead  is  capable  of  decomposing  water,  and  when  sufffied  to  stanch 
'long  in  a  vessel  uflliis  metal,  it  becomes  poisonous.     When  used 
•y  to  convey  water,  there  is  but  little  danger.     C, 

•14* 


150  METALS* 

Mrs.  B.  Yes.  But  there  is  another  important  connection 
between  metals  and  acids,  with  which  I  must  now  make  you 
acquainted.  Metals,  when  in  the  state  of  oxyds,  are  capable 
of  being  dissolved  by  acids.  In  this  operation  they  enter  into 
a  chemical  combination  with  the  acid,  and  form  an  entirely 
new  compound. 

Caroline.  But  what  difference  is  there  between  the  oxy ela- 
tion and  the  dissolution  of  the  metal  by  an  acid  ? 

Mrs.  B.  In  the  first  case,  the  metal  merely  combines  with  a 
portion  of  oxygen  taken  from  the  acid,  which  is  thus  partly  de- 
oxygenated,  as  in  the  instance  you  have  just  seen ;  in  the  second 
case,  the  metal,  after  being  previously  oxydated,is  actually  dissol- 
ved in  the  acid,  and  enters  into  a  chemical  combination  with  it, 
without  producing  any  further  decomposition  or  effervescence. 
— This  complete  combinati  n  of  an  oxyd  and  an  acid  forms  a 
peculiar  and  important  class  of  compound  salts. 

Emily.  The  difference  between  an  oxyd  and  a  compound 
salt,  therefore,  is  very  obvious  ;  the  one  consists  of  a  metal  and 
oxygen  ;  the  other  of  an  oxyd  and  an  acid. 

Mrs.  B.  Very  well :  and  you  will  be  careful  to  remember 
that  the  metals  are  incapable  of  entering  into  this  combination 
with  acids,  unless  they  are  previously  oxydated ;  therefore., 
whenever  you  bring  a  metal  in  contact  with  an  acid,  it  will  be 
first  oxydated  and  afterwards  dissolved,  provided  that  there  be 
a  sufficient  quantity  of  acid  for  both  operations. 

There  are  some  metals,  however,  whose  solution  is  more  ea- 
sily accomplished,  by  diluting  the  acid  in  water;  and  the  metal 
will,  in  this  case,  be  oxydated,  not  by  the  acid,  but  by  the  wa- 
ter, which  it  will  decompose.  But  in  proportion  as  the  oxygen 
of  the  water  oxydates  the  surface  of  the  metal,  the  acid  corn- 
bines  with  it,  washes  it  off,  and  leaves  a  fresh  surface  for  the 
oxygen  to  act  upon :  then  other  coats  of  oxyd  are  successively 
'formed,  and  rapidly  dissolved  by  the  acid,  which  continues 
combining  with  the  new-formed  surfaces  of  oxyd  till  the  whole 
of  -the  metal  is  dissolved.  During  this  process  the  hydrogen 
gas  of  the  water  is  disengaged,  and  flies  off  with  effervescence. 

Emily.  Was  not  this  the  manner  in  which  the  sulphuric  acid 
assisted  the  iron  filings  in  decomposing  water  ? 

Airs.  B.  Exactly  ;  and  it  is  thus  that  several  metals,  which 
are  incapable  alone  of  decomposing  water,  are  enabled  to  do 
it  by  the  assistance  of  an  acid,  which,  by  continually  washing 
off  the  covering  of  oxyd,  as  it  is  formed,  prepares  a  fresh  sur- 
face of  metal  to  act  upon  the  water. 

Caroline.  The  acid  here  seems  to  act  a  part  not  very  differ' 


METALS.  151 

ent  from  that  of  a  scrubbing-brush. — But  pray  would  not  this 
be  a  good  method  of  cleaning  metallic  utensils  ? 

Mrs.  B.  Yes ;  on  some  occasions  a  weak  acid,  as  vinegar, 
is  used  for  cleaning  copper.  Iron  plates,  too,  are  freed  from 
the  rust  on  their  surface  by  diluted  muriatic  acid,  previous  to 
their  being  covered  with  tin.  You  must  remember,  however5 
that  in  this  mode  of  cleaning  metals  the  acid  should  be  quickly 
afterwards  wiped  off,  otherwise  it  would  produce  fresh  oxyd. 

Caroline.  Let  us  watch  the  dissolution  of  the  copper  in  the 
nitric  acid  ;  for  I  am  very  impatient  to  see  the  salt  that  is  to  re- 
sult from  it.  The  mixture  is  now  of  a  beautiful  blue  colour  5 
but  there  is  no  appearance  of  the  formation  of  a  salt;  it  seems 
to  be  a  tedious  operation. 

Mrs.  B.  The  crystallisation  of  the  salt  requires  some  length 
of  time  to  be  completed  ;  if,  however,  you  are  so  impatient,  I 
can  easily  show  you  a  metallic  salt  already  formed. 

Caroline.  But  that  would  not  satisfy  my  curiosity  half  so 
well  as  one  of  our  own  manufacturing. 

Mrs.  B.  It  is  one  of  our  own  preparing  that  I  mean  to  show 
you.  When  we  decomposed  water  a  few  days  since,  by  the 
oxydation  of  iron  filings  through  the  assistance  of  sulphuric 
acid,  in  what  did  the  process  consist  ? 

Caroline.  In  proportion  as  the  water  yielded  its  oxygen  to 
the  iron,  the  acid  combined  with  the  new-formed  oxyd,  and  the 
hydrogen  escaped  alone. 

Mrs.  B.  Very  well ;  the  result,  therefore,  was  a  compound 
salt,  formed  by  the  combination  of  sulphuric  acid  with  oxyd  of 
iron.  It  still  remains  in  the  vessel  in  which  the  experiment 
was  performed.  Fetch  it,  and  we  shall  examine  it. 

Emily.  What  a  variety  of  processes  the  decomposition  of  wa- 
ter, by  a  mutfll  and  an  acid,  implies  :  1st,  the  decomposition  of 
the  water  ;  2d)y,  the  oxydation  of  the  metal;  and  3dly,  the 
formation  of  a  compound  salt. 

Caroline.  Here  it  is,  Mrs.  B. — What  beautiful  green  crys- 
tals !  But  we  do  not  perceive  any  crystals  in  the  solution  of 
copper  in  nitrous  acid  ? 

Mrs.  B.  Because  the  salt  is  now  suspended  in  the  water 
which  the  nitrous  acid  contains,  and  will  remain  so  till  it  is  de- 
posited in  consequence  of  rest  and  cooling. 

Emily.  I  am  surprised  that  a  body  so  opaque  as  iron  can  be 
converted  into  such  transparent  crystals. 

Mrs.  B.  It  is  the  union  with  the  acid  that  produces  the  trans* 
parency ;  for  if  the  pure  metal  were  melted,  and  afterwards 
permitted  to  cool  and  crystallise,  it  would  be  found  just  as 
opaque  as  before. 


152  METALS, 

Emily.  I  do  not  understand  the  exact  meaning  of  crystallisa- 
tion. 

Mrs.  B.  You  recollect  that  when  a  solid  body  is  dissolved 
either  by  water  or  caloric  it  is  not  decomposed  ;  but  that  its  in- 
tegrant parts  are  only  suspended  in  the  solvent.  When  the  so- 
lution is  made  in  water,  the  integrant  particles  of  the  body  will, 
on  the  water  being  evaporated,  again  unite  into  a  solid  mass  by 
the  force  of  their  mutual  attraction.  But  when  the  body  is  dis- 
solved by  caloric  alone,  nothing  more  is  necessary,  in  order  to 
make  its  particles  re-unite,  than  to  reduce  its  temperature.  And, 
in  general,  if  the  solvent,  whether  water  or  caloric,  be  slowly 
separated  by  evaporation  or  by  cooling,  and  care  taken  that 
the  particles  be  not  agitated  during  their  re-union,  they  will  ar- 
range themselves  in  regular  masses,  each  individual  substance 
assuming  a  peculiar  form  or  arrangement;  and  this  is  what  is 
called  crystallisation. 

Emily.  Crystallisation,  therefore,  is  simply  the  re-union  of 
the  particles  of  a  solid  body  which  has  been  dissolved  in  a 
fluid.* 

Mrs.  B.  That  is  a  very  good  definition  of  it.  But  I  must 
not  forget  to  observe,  that  heat  and  water  may  unite  their  sol- 
vent powers  5  and,  in  this  case,  crystallisation  may  be  hasten- 
ed by  cooling,  as  well  as  by  evaporating  the  liquid. 

Caroline.  But  if  the  body  dissolved  is  of  a  volatile  nature, 
will  it  not  evaporate  with  the  fluid  ? 

Mrs.  13.  A  crystallised  body  held  in  solution  only  by  water 
is  scarcely  ever  so  volatile  as  the  fluid  itself,  and  care  must  be 
taken  to  manage  the  heat  so  that  it  may  be  sufficient  to  evapo- 
rate the  water  only 

I  should  not  omit  also  to  mention  that  bodies,  in  crystallising 
from  their  watery  solution,  always  retain  a  small  portion  of 
water,  which  remains  confined  in  the  crystal  in  a  solid  form, 
and  does  not  re-appear  un^es  the  body  loses  it  crystalline  state. 

This  is  called  the  water  of  crystallisation.  But  you  must 
observe,  that  whilst  a  body  may  be  separated  from  its  solution 
in  water  or  caloric  simply  by  cooling  or  by  evaporation,  an  acid 
can  be  taken  from  a  metal  with  which  it  is  combined  only  by 
stronger  affinities,  which  produce  a  decomposition. 

Emily  Are  the  perfect  metals  susceptible  of  being  dissolved 
and  converted  into  compound  salts  by  acids  ? 

Mrs.  B.  Gold  is  acted  upon  by  only  one  acid,  the  oxygena- 

*  Not  exactly,  because  the  particles  of  the  fluid  make  a  part  of  the 
crystal.  Crystallisation  is  that  process  by  which  the  particles  of  !1?v 
flies  unite  to  form  solids,  of  certain,  and  regular  shapes.  C. 


METALS.  15^ 

fed  muriatic,  a  very  remarkable  acid,  which,  when  in  its  most 
concentrated  state,  dissolves  gold  vsr  any  other  metal,  by  burn- 
ing them  rapidly. 

Gold  can,  it  is  true,  be  dissolved  likewise  by  a  mixture  of 
two  acids,  commonly  called  aqua  regia  ;  but  this  mixed  solv- 
ent derives  that  property  from  containing  the  peculiar  acid 
which  I  have  just  mentioned.  Platina  is  also  acted  upon  by 
this  acid  only ;  silver  is  dissolved  by  nitric  acid. 

Caroline.  I  think  you  said  that  some  of  the  metals  might  be 
so  strongly  oxydated  as  to  become  acid  ? 

Mrs.  B.  There  are  five  metals,  arsenic,  molybdena,  chrome, 
tungsten,  and  columbium,  which  are  susceptible  of  combining 
with  a  sufficient  quantity  of  oxygen  to  be  converted  into  acids. 

Caroline.  Acids  are  connected  with  metals  in  such  a  varie- 
ty of  ways,  that  I  am  afraid  of  some  confusion  in  remembering 
them. — In  the  first  place,  acids  will  yield  their  oxygen  to  met- 
als. Secondly,  they  will  combine  with  them  in  their  state  of 
oxyds,  to  form  compound  salts;  and  lastly^  several  of  the  met- 
als are  themselves  susceptible  of  acidification. 

Mrs.  B.  Very  well ;  but  though  metals  have  so  great  an  af- 
finity for  acids,  it  is  not  with  that  class  of  bodies  alone  that  they 
will  combine.  They  are  most  of  them  in  their  simple  state? 
capable  of  uniting  with  sulphur,  with  phosphorus,  with  carbon, 
and  with  each  other;  these  combinations,  according  to  the  no- 
menclature which  was  explained  to  you  on  a  former  occasion, 
are  called  sulphurets,  pkosphoretg,  carburets,  &c. 

The  metallic  phosphorets  offer  nothing  very  remarkable. 
The  sulphurets  form  the  peculiar  kind  of  mineral  called  pyrites^ 
from  which  certain  kinds  of  .mineral  \vaters>  as  those  of  Ilarro 
2;ate,  derive  their  chief  chemical  properties.  In  this  combina- 
lion,  the  sulphur,  together  with  the  iron,  have  so  strong  an  at- 
traction for  oxygen,  that  they  obtain  it  both  from  the  air  and 
from  Water,  and  by  condensing  it  in  a  solid  form,  produce  the 
heat  which  raises  the  temperature  of  the  water  in  such  a  re- 
markable degree. 

Emily.  But  if  pyrites  obtain  oxygen  from  water,  that  water- 
must  suffer  a  decomposition,  and  hydrogen  gas  be  evolved. 

Mrs.  B.  That  is  actually  the  case  in  the  hot  sgrings  alluded 
to,  which  give  out  an  extremely  fetid  gas,  composed  of  hydro* 
gen  impregnated  with  sulphur. 

Caroline.  If  I  recollect  right,  steel  and  plumbago,  which 
you  mentioned  in  the  last  lesson,  are  both  carburets  of  iron  ? 

Mrs.  B.  Yes ;  and  they  are  the  only  carburets  of  much  con- 
sequence. 

\  curious  combination  of  metals  has  lately  very  much  at- 


154  METALS. 

tracted  the  attention  of  the  scientific  world  :  I  mean  the  mete 
oric  stones  which  fall  from  the  atmosphere.  They  consist  prin- 
cipally of  native  or  pure  iron,  which  is  never  found  in  that  state 
in  the  bowels  of  the  earth*  and  contain  also  a  small  quantity  of 
nickel  and  chrome,  a  combination  likewise  new  in  the  mineral 
kingdom* 

These  circumstances  have  led  many  scientific  persons  to  be- 
lieve that  those  substances  have  fallen  from  the  moon,  or  some 
other  planet,  while  others  are  of  opinion  either  that  they  are 
formed  in  the  atmosphere,  or  are  projected  into  it  by  some  un- 
known volcano  on  the  surface  of  our  globe. 

Caroline.  I  have  heard  much  of  these  stones,  but  I  believe 
many  people  are  of  opinion  that  they  are  formed  on  the  surface 
of  the  earth,  and  laugh  at  their  pretended  celestial  origin. 

Mrs.  B.  The  fact  of  their  falling  is  so  well  ascertained,  that 
1  think  no  person  who  has  at  all  investigated  the  subject,  can 
now  entertain  any  doubt  of  it.  Specimens  of  these  stones  have 
been  discovered  in  all  parts  of  the  world,  and  to  each  of  them 
some  tradition  or  story  of  its  fall  has  i>cen  found  connected. 
And  as  the  analysis  of  all  those  specimens  affords  precisely  the 
same  results,  there  is  strong  reason  to  cor.jrcture  that  they  all 
proceed  from  the  same  source.  It  is  to  Mr,  Howard  that  phi- 
losophers are  indebted  for  having  firs-t  analysed  these  stones, 
and  directed  their  attention  to  this  interesting  subject. 

Candine.  But  pray,  Mrs.  B.,  how  can  solid  masses  of  nick- 
el be  formed  from  the  atmosphere,  which  consists  of  the  t\\  c 
airs,  nitrogen  and  oxygen  ? 

Mrs.  B.  I  really  do  not  see  how  they  could,  ^and  think  it 
much  more  nrobable  that  they  fall  from  tb*  ™"on.  or  some  oth- 
er celestial  body. — But  we  must  not  suffer  this  digression  to 
take  up  too  much  of  our  time. 

The  combinations  of  metals  with  each  other  are  called  alloys  j; 

*  This  seems  to  be  a  mistake.  Several  localities  of  native  iron, 
found  in  veins  are  pointed  out  by  auihors.  In  several  instances  large 
blocks  of  native  iron  have  been  found  on  the  surface  of  the  earth.  Onp 
found  by  Prof.  Pallas  in  Siberia  weighed  loUU  Jus.  Another  found  in 
South  America  is  sad  to  weigh  30,000  Ibs.  &c.  Those  have  been  sus- 
pected to  be  of  meteoric  origin,  though  nothing  is  known,  which  inak^s. 
this  certain.  Those  stones  which  are  known  beyond  a  doubt  to  have 
fallen  from  the  atmosphere,  have  a  very  different  composition.  These 
generally  contain  the  following  ingredients,  viz.  iron,  nickel  chrome, 
oxide  of  iron,  sulphur,  silex,  lime,  mugnesia,  and  alumine.  The  iron 
rarely  amounts  to  a  quarter  of  the  whole.  Accounts  are  recorded  of 
the  falling  of  stones,  sulphur,  &c.  in  every  age  since  the  Christian  era, 
and  in  almost  every  part  of  the  world.-  C. 


METALS.  155 

thus  brass  is  an  alloy  of  copper  and  zinc ;  bronze,  of  copper 
and  tin,  &c. 

Emily.  And  is  not  pewter  also  a  combination  of  metal  ? 

Mrs.'  B.  It  is.  The  pewter  made  in  this  country  is  most- 
ly composed  of  tin,  with  a  very  small  proportion  of  zinc  and 
lead. 

Caroline.  Block-tin  is  a  kind  of  pewter,  I  believe  ? 

Mrs.  B.  Properly  speaking,  block-tin  means  tin  in  blocks, 
or  square  massive  ingots  ;  but  in  the  sense  in  which  it  is  used 
by  ignorant  workmen,  it  is  iron  plated  with  tin,  which  renders 
it  more  durable,  as  tin  will  not  so  easily  rust.  Tin  alone,  how- 
ever, would  be  too  soft  a  metal  to  be  worked  for  common  use, 
and  all  tin  vessels  and  utensils  are  in  fact  made  of  plates  of 
iron,  thinly  coated  with  tin,  which  prevents  the  iron  from  rusting. 

Caroline.  Say  rather  oxydating,  Mrs.  B. — Rust  is  a  word 
that  should  be  exploded  in  chemistry. 

Mrs.  li.  Take  care,  however,  not  to  introduce  the  word  ox- 
y  el  ate,  instead  of  rust,  in  general  conversation  ;  for  you  would 
probably  not  be  understood,  and  you  might  be  suspected  of  af- 
fectation. 

Metals  differ  very  much  in  their  affinity  for  each  other ;  some 
will  not  unite  at  all,  others  readily  combine  together,  and  on 
this  property  of  metals  the  art  of  soldering  depends. 

Emily.  What  is  soldering  ? 

Mrs.  />.  It  is  joining  two  pieces  of  metal  together,  by  a  more 
fusible  metal  interposed  between  them.  Thus  tin  is  a  solder 
for  lead ;  brass,  gold,  or  silver,  are  solder  for  iron,  &c. 

Caroline.  And  is  not  plating  metals  something  of  the  same 
nature  ? 

Mrs.  B.  In  the  operation  of  plating,  two  metals  are  uni'ed, 
one  being  covered  with  the  other,  but  without  the  intervention 
of  a  third  ;  iron  or  copper  may  thus  be  covered  with  gold  or 
silver. 

Emily.  Mercury  appears  to  me  of  a  very  different  nature 
from  the  other  metals. 

Mrs.  B.  One  of  its  greatest  peculiarities  is,  that  it  retains  a 
fluid  state  at  the  temperature  of  the  atmosphere.  All  metals 
are  fusible  at  different  degrees  of  heat,  and  they  have  likewise 
each  the  property  of  freezing  or  becoming  solid  at  a  certain  fix- 
ed temperature.  Mercury  congeals  only  at  seventy-two  degrees 
below  the  freezing  point. 

Emily.  That  is  to  say,  that  in  order  to  freeze,  it  requires  a 
temperature  of  seventy-two  degrees  colder  than  that  at  which 
water  freezes. 

Mrs.  B.  Exactly  so. 


15  METALS. 

Caroline.  But  is  the  temperature  of  the  atmosphere  ever  sw 
low  as  that  ? 

Mrs.  B.  Yes,  often  in  Siberia  ;  but  happily  never  in  this 
part  of  the  globe.  Here,  however,  mercury  may  be  congealed 
by  artificial  cold  ;  I  mean  such  intense  cold  as  can  be  produced 
by  some  chemical  mixtures,  or  by  the  rapid  evaporation  of 
ether  under  the  air  pump.* 

Caroline.     And  can  mercury  be  made  to  boil  and  evaporate  ? 

•Mrs.  /).  Yes,  like  any  other  liquid  j  only  it  requires  a  much 
greater  degree  of  heat.  At  the  temperature  of  six  hundred 
degrees,  it  begins  to  boil  and  evaporate  like  water. 

Mercury  combines  with  gold,  silver,  tin,  and  with  several  oth- 
er metals ;  and,  if  mixed  with  any  of  them  in  a  sufficient  pro- 
portion, it  penetrates  the  solid  metal,  softens  it,  loses  its  own  flu- 
idity, and  forms  an  amalgam,  which  is  the  name  given  to  the 
combination  of  any  metal  with  mercury,  forming  a  substance 
more  or  less  solid,  according  as  the  mercury  or  the  other  metal 
predominates. 

Emily.  In  the  list  of  metals  there  are  some  whose  names  I 
have  never  before  heard  mentioned. 

Mrs.  B.  Besides  those  which  Sir  H.  Davy  has  obtained, 
there  are  several  that  have  been  recently  discovered,  whose 
properties  are  yet  but  little  known,  as  for  instance,  titanium, 
which  was  discovered  by  the  Rev.  Mr.  Gregor,  in  the  tin-mines 
of  Cornwall ;  columbium  or  tantalium,  which  has  lately  been 
discovered  by  Mr.  Hatchett ;  and  osmium,  iridium,  palladium, 
and  rhodium,  all  of  which  Dr.  Wollaston  and  Mr.  Tennant 
found  mixed  in  minute  quantities  with  crude  platina,  and  the 
distinct  existence  of  which  they  proved  by  curious  and  delicate 
experiments.  More  recently  still  Professor  Parhelius  has  dis- 
covered in  a  pyritic  ore,  at  Fahlun,  in  Sweden,  a  metallic  sub- 
stance, which  he  has  called  selenium,  and  which  has  the  singu- 
lar peculiarity  of  assuming  the  form  of  a  yellow  gas  when  heat- 
ed in  close  vessels.  In  some  of  its  properties  this  substance 
seems  to  hold  a  medium  between  the  combustibles  and  the  met- 
als. It  bears  in  particular  a  strong  analogy  to  sulphur. 

Caroline.  Arsenic  has  been  mentioned  amongst  the  metals,  I 
had  no  notion  that  it  belonged  to  that  class  of  bodies,  for  I  had 
never  seen  it  but  as  a  powder,  and  never  thought  of  it  but  as  a 
most  deadly  poison. 

.--.rs.  B.  In  its  pure  metallic  state,  I  believe,  it  is  not  so  poi- 
sonous; but  it  has  such  a  great  affinity  for  oxygen,  that  it  ab- 

*  By  a  process  analogous  to    that  described,  page  72,  of  thie  yol- 


Mhl'ALs.  15 

b-urbs  it  iVom  tiie  atmosphere  at  its  natural  temperature  :  you 
have  seen  it,  therefore,  only  in  its  state  of  oxyd,  when,  from  its 
combination  with  oxygen,  it  has  acquired  its  very  poisonous 
properties. 

Caroline.  Is  it  possible  that  oxygen  can  impart  poisonous 
qualities  ?  That  valuable  substance  which  produces  light  and 
iire,  and  which  all  bodies  in  nature  are  so  eager  to  obtain  ? 

Mrs.  B.  Most  of  the  metallic  oxyds  are  poisonous,  and  de- 
rive this  property  from  their  union  with  oxygen.  The  white 
lead,  so  much  used  in  paint,  owes  its  pernicious  effects  to  oxy- 
gen. In  general,  oxygen,  in  a  concrete  state,  appears  to  be 
particularly  destructive  in  its  effects  on  flesh  or  any  animal  mat- 
ter ;  and  those  oxyds  are  most  caustic  that  have  an  acrid  burn- 
ing taste,  which  proceeds  from  the  metal  having  but  a  slight  af- 
iinity  for  oxygen,  and  therefore  easily  yielding  it  to  the  fleshs 
which  it  corrodes  and  destroys. 

Emily.  What  is  the  meaning  of  the  word  caustic,  which  you 
have  just  used  ? 

Mrs.  B.  It  expresses  that  property  which  some  bodies  pos- 
sess, of  disorganizing  and  destroying  animal  matter,  by  ope- 
rating a  kind  of  combustion,  or  at  least  a  chemical  decomposi- 
tion. You  must  often  have  heard  of  caustic  used  to  burn  warts, 
or  other  animal  excrescences ;  most  of  these  bodies  owe  their 
destructive  power  to  the  oxygen  with  which  they  are  combined. 
The  common  caustic,  called  lunar  caustic,  is  a  compound  form- 
ed by  the  union  of  nictric  acid  and  silver  :  and  it  is  supposed 
to  owe  its  caustic  qualities  to  the  oxygen  contained  in  the  nitric 
acid. 

Caroline.  But,  pray,  are  not  acids  still  more  caustic  than 
oxyds,  as  they  contain  a  greater  proportion  of  oxygen  ? 

Mrs.  l<.  Some  of  the  acids  are  ;  but  the  caustic  property  of 
a  body  depends  not  only  upon  the  quantity  of  oxygen  which  it 
contains,  but  also  upon  its  slight  affinity  for  that  principle,  and 
the  consequent  facility  with  which  it  yields  it. 

Emily.  Is  not  this  destructive  property  of  oxygen  accounted 
for? 

Mrs.  B.  It  proceeds  probably  from  the  strong  attraction  of 
oxygen  for  hydrogen  ;  for  if  the  one  rapidly  absoib  the  other 
from  the  animal  fibre,  a  disorganization  of  the  substance  must 
ensue. 

Emily.  Caustics  are,  then,  very  properly  said  to  burn  the 
flesh,  since  the  combination  of  oxygen  and  hydrogen  is  an  ac- 
tual combustion. 

Caroline.  Now,  I  think,  this  effect  would  be  more  properly 


158  METALS. 

termed  an  oxydation,  as  there  is  no  disengagement  of  light  and 
heat. 

Mrs.  B.  But  there  really  is  a  sensation  of  heat  produced  by 
the  action  of  caustics. 

Emily.  If  oxygen  is  so  caustic,  why  does  not  that  which  is 
contained  in  the  atmosphere  burn  us  ? 

Mrs.  B.  Because  it  is  in  a  gaseous  state,  and  has  a  greater 
attraction  for  its  electricity  than  for  the  hydrogen  of  our  bodies.' 
Besides,  should  the  air  be  slightly  caustic,  we  are  in  a  great 
measure  sheltered  from  its  effects  by  the  skin  ;  you  know  how 
much  a  wound,  however  trifling,  smarts  on  being  exposed 
to  it. 

Caroline.  It  is  a  curious  idea,  however,  that  we  should  live 
in  a  slow  fire.  But  if  the  air  was  caustic,  would  it  not  have 
an  acrid  taste  ? 

Mrs.  B.  It  possibly  may  have  such  a  taste,  though  in  so 
slight  a  degree,  that  custom  has  rendered  it  insensible. 

Caroline.  And  why  is  not  water  caustic  ?  When  I  dip  ray 
hand  into  water,  though  cold,  it  ought  to  burn  me  from  the 
caustic  nature  of  its  oxygen. 

Mrs.  B.  Your  hand  does  not  decompose  the  water;  the  ox- 
ygen in  that  state  is  much  better  supplied  with  hydrogen  than 
it  would  be  by  animal  matter,  and  if  its  causticity  depend  on 
its  affinity  for  that  principle,  it  will  be  very  far  from  quitting 
its  state  of  water  to  act  upon  your  hand.  You  must  not  forget 
that  oxyds  are  caustic  in  proportion  as  the  oxygen  adheres 
slightly  to  them. 

Emily.  Since  the  oxyd  of  arsenic  is  poisonous,  its  acid,  I 
suppose,  is  fully  as  much  so  ? 

Airs.  B.  Yes  ;  it  is  one  of  the  strongest  poisons  in  nature. 

Emily.  There  is  a  poison  called  verdigris,  which  forms  on 
brass  and  copper,  when  not  kept  very  clean  ;  and  this,  I  have 
heard,  is  an  objection  to  these  metals  being  made  into  kitchen 
utensils.  Is  this  poison  likewise  occasioned  by  oxygen  ? 

Mrs.  B.  It  is  produced  by  the  intervention  of  oxygen  ;  for 
verdigris  is  a  compound  salt  formed  by  the  union  of  vinegar  and 
copper ;  it  is  of  a  beautiful  green  colour,  and  much  used  in 
painting. 

Emily.  But,  I  believe,  verdigris  is  often  formed  on  copper 
when  no  vinegar  has  been  in  contact  with  it. 

Mi's.  B.  Not  real  verdigris,  but  other  salts,  somewhat  re- 
sembling it,  may  be  produced  by  the  action  of  other  acids  on 
copper. 

The  solution  of  copper  in  nitric  acid,  if  evaporated,  affords 
a  salt  which  produces  an  effect  on  tin  that  will  surprise  you, 


METALis*  15 

and  I  have  prepared  some  from  the  solution  we  made  before, 
that  I  might  show  it  to  you.  -I  shall  first  sprinkle  some  water  on 
this  piece  of  tin-foil,  and  then  some  of  the  salt. — Now  observe 
that  1  fold  it  up  suddenly,  and  press  it  into  one  lump. 

Caroline.  What  a  prodigious  vapour  issues  from  it — and 
sparks  of  fire  I  declare  ! 

Mrs.  B.  I  thought  it  would  surprise  you.  The  effect,  how- 
ever, I  dare  say  you  could  account  for,  since  it  is  merely  the 
consequence  of  the  oxygen  of  the  salt  rapidly  entering  into  a 
closer  combination  with  the  tin. 

There 4s  also  a  beauttful  green  salt  too  curious  to  be  omitted; 
it  is  produced  by  the  combination  of  cobalt  with  muriatic  acid, 
which  has  the  singular  property  of  forming  what  is  called  sym- 
pathetic ink.  Characters  written  with  this  solution  are  invisi- 
ble when  cold,  but  when  a  gentle  heat  is  applied,  they  assume  a 
fine  bluish  green  colour. 

Caroline.  I  think  one  might  draw  very  curious  landscapes 
with  the  assistance  of  this  ink  ;  I  would  first  make  a  water-col- 
our drawing  of  a  winter-scene,  in  which  the  trees  should  be 
leafless,  and  the  grass  scarcely  green  ;  I  would  then  trace  all 
ihe  verdure  with  the  invisible  ink,  and  whenever  I  chose  to  cre- 
ate spring,  I  should  hold  it  before  the  fire,  and  its  warmth 
would  cover  the  landscape  with  a  rich  verdure. 

Mrs.  i>.  That  will  be  a  very  amusing  experiment,  and  I 
advise  you  by  all  means  to  try  it. 

Before  we  part,  I  must  introduce  to  your  acquaintance  the 
curious  metals  which  Sir  H.  Davy  has  recently  discovered. 
The  history  of  these  extraordinary  bodies  is  yet  so  much  in  its 
infancy,  that  I  shall  confine  myself  to  a  very  short  account  of 
them  5  it  is  more  important  to  point  out  to  you  the  vast,  and 
apparently  inexhaustable,  field  of  research  which  has  been 
thrown  open  to  our  view  by  Sir  H.  Davy;s  memorable  discov- 
eries, than  to  enter  into  a  minute  account  of  particular  bodies  or 
experiments. 

Caroline.  But  I  have  heard  that  these  discoveries,  however 
splendid  and  extraordinary,  are  jiot  very  likely  to  prove  of  any 
great  benefit  to  the  world,  as  they  are  rather  objects  of  curiosi- 
ty than  of  use. 

Mrs.  E.  Such  may  be  the  illiberal  conclusions  of  the  igno- 
rant and  narrow-minded  ;  but  those  who  can  duly  estimate  the 
advantages  of  enlarging  the  sphere  of  science,  must  be  convinc- 
ed that  the  acquisition  of  every  new  fact,  however  unconnect- 
ed it  ma}'  at  first  appear  with  practical  utility,  must  ultimately 
prove  beneficial  to  mankind.  But  these  remarks  are  sc  ircely 
applicable  to  the  present  subject ;  for  some  of  the  new  metals 


160  PETALS. 

have  already  proved  eminently  useful  as  chemical  agents,  ana 
are  likely  soon  to  be  employed  in  the  arts.  For  the  enumera- 
tion of  these  metals,  I  must  refer  you  to  our  list  of  simple  bod- 
ies; they  are  derived  from  the  alkalies,  the  earths,  and  three 
of  the  acids,  all  of  which  h.id  been  hitherto  considered  as  un- 
decompoundable  or  simple  bodies. 

When  Sir  H.  Davy  first  turned  h»s  attention  to  the  effects  of 
the  Voltaic  baitery,  he  tried  its  power  on  a  variety  of  compound 
bodies,  and  gradually  brought  to  light  a  number  of  new  and  in- 
teresting facts,  which  led  the  way  to  more  important  discove- 
ries. It  would  be  highly  interesting  to  trace  his  steps  in  this 
new  department  of  science,  but  it  would  lead  us  too  far  from 
our  principal  object.  A  general  view  of  his  most  remarkable 
discoveries  is  all  that  I  can  aim  at,  or  that  you  could,  at  present, 
understand. 

The  facility  with  which  compound  bodies  yielded  to  the 
Voltaic  electricity,  induced  him  to  make  trial  of  its  effects  on 
substances  hitherto  considered  as  simple,  but  which  he  suspect- 
ed of  being  compound,  and  his  researches  were  soon  crowned 
with  the  most  complete  success. 

The  body  which  he  first  submitted  to  the  Voltaic  battery, 
and  which  had  never  yet  been  decomposed,  was  one  of  the  fix- 
ed alkalies,  called  potash.  This  substance  gave  out  an  elastic 
fluid  at  the  positive  wire,  which  was  ascertained  to  be  oxygen, 
and  at  the  negative  wire,  small  globules  of  a  very  high  metallic 
lustre,  very  similar  in  appearance  to  mercury;  thus  proving 
that  potash,  which  had  hitherto  been  considered  as  a  simple 
incombustible  body,  was  in  fact  a  metallic  oxyd  ;  and  that  its 
incombustibility  proceeded  from  its  being  already  combined 
with  oxygen. 

Emily-  I  suppose  the  wires  used  in  this  experiment  were  of 
platina,  as  they  were  when  you  decomposed  water ;  for  if  of 
iron,  the  oxygen  would  have  combined  with  the  wire,  instead  of 
appearing  in  the  form  of  gas. 

Mrs.  B.  Certainly :  the  metal,  however,  would  equally  have 
been  disengaged.  SirH.  Davy  has  distinguished  this  new  sub- 
stance by  the  name  of  POTASSIUM,  which  is  derived  from  that 
of  the  alkali,  from  which  it  is  procured.  I  have  some  small 
pieces  of  it  in  this  phial,  but  you  have  already  seen  it,  as  it  is 
the  metal  which  we  burnt  in  contact  with  sulphur. 

Emily.  What  is  the  liquid  in  which  you  keep  it  ? 

Mrs.  J3.  It  is  naptha,  a  bituminous  liquid,  with  which  I  shall 
hereafter  make  you  acquainted.  It  is  almost  the  only  fluid  in 
which  potassium  can  be  preserved,  as  it  contains  no  oxygen, 


METALS.  101 

and  this  metal  has  so  powerful  an  attraction  for  oxygen,  that 
it  will  not  only  absorb  it  from  the  air,  but  likewise  from  water, 
or  any  body  whatever  that  contains  it. 

Emily.  Tiiis,  then,  is  one  of  the  bodies  that  oxydates  spoit- 
laneousiy  without  the  application  of  heat  ? 

Mrs.  B.  Yes  ;  and  it  has  this  remarkable  peculiarity,  that 
it  attracts  oxygen  much  more  rapidly  from  water  than  from  air  j 
so  that  when  thrown  into  water,  however  cold,  it  actually  bursts 
into  flame.  I  shall  now  throw  a  small  piece,  about  the  size  of 
a  pin's  head,  on  this  drop  of  water. 

Caroline.  It  instantaneously  exploded,  producing  a  little  flash 
of  light  !  this  is,  indeed,  a  most  curious  substance  ! 

Mrs.  B.  By  its  combustion  it  is  re-converted  into  potash  ;  and 
as  potash  is  now  decidedly  a  compound  body,  I  shall  not  enter 
into  any  of  its  properties  till  we  have  completed  our  review  of 
the  simple  bodies;  but  we  may  here  make  a  few  observations 
on  its  basis,  potassium.  If  this  substance  is  left  in  contact  with 
air,  it  rapidly  returns  to  the  state  of  potash,  with  a  disengage- 
ment of  heat,  but  without  any  flash  of  light. 

Emily.  But  is  it  not  very  singular  that  it  should  burn  better 
in  water  than  in  air? 

Caroline.  I  do  not  think  so :  for  if  the  attraction  of  potas- 
sium for  oxygen  is  so  strong  that  it  finds  no  more  difficulty  in 
separating  it  from  the  hydrogen  in  water,  than  in  absorbing  it 
from  the  air,  it  will  no  doubt  be  more  amply  and  rapidly  sup- 
plied by  water  than  by  air. 

Mrs.  B.  That  cannot,  however,  be  precisely  the  reason,  fot 
when  potassium  is  introduced  under  water,  without  contact  of 
air,  the  combustion  is  not  so  rapid,  and  indeed,  in  that  case, 
there  is  no  luminous  appearance;  but  a  violent  action  takes 
place,  much  heat  is  excited,  the  potash  is  regenerated,  and  hy- 
drogen gas  is  evolved. 

Potassium  is  so  eminently  combustible,  that  instead  of  requi- 
rins,  like  other  metals,  an  elevation  of  temperature,  it  will  f.urii 
rapidly  in  contact  with  water,  even  below  the  freezing  poifif. 
This  you  may  witness  by  throwing  a  piece  on  this  lump  of  ice. 

Caroline.  It  again  exploded  with  flame,  and  has  made  u 
•Jeep  hoi*3  in  the  ice.  • 

Mrs.  B.  This  hole  contains  a  solution  of  potash  ;  for  the  al- 
kali being  extremely  soluble,  disappears  in  the  wat^r  at  the  in- 
stant it  is  produced.  Its  presence,  however,  may  be  easily  as- 
certained, alkalies  having  the  property  of  changing  paper5 
stained  with  turmeric,  to  a  red  colour  ;  if  you  dip  one  end  of 
this  slip  of  paper  into  the  hole  in  the  ice  you  will  see  i< 

15* 


162  METALS, 

colour,  and  the  same,  if  you  wet  it  with  the  drop  of  water  in 
which  the  first  piece  of  potassium  was  burnt. 

Caroline.  It  has  indeed  changed  the  paper  from  yellow  to 
red. 

Mrs.  B.  This  metal  will  burn  likewise  in  carbonic  acid  gas, 
a  gas  that  had  always  been  supposed  incapable  of  supporting 
combustion,  as  we  were  unacquainted  with  any  substance  that 
had  a  greater  attraction  for  oxygen  than  carbon.  Potassium, 
however,  readily  decomposes  this  gas,  by  absorbing  its  oxy- 
gen, as  I  shall  show  you.  This  retort  is  filled  with  carbonic 
acid  gas. — I  will  put  a  small  piece  of  potassium  in  it ;  but  for 
this  combustion  a  slight  elevation  of  temperature  is  required, 
for  which  purpose  I  shall  hold  the  retort  over  the  lamp. 

Caroline.  Now  it  has  taken  fire,  and  burns  with  violence ! 
It  has  burst  the  retort. 

Mrs.  B.  Here  is  the  piece  of  regenerated  potash ;  can  you 
tell  me  why  it  has  become  so  black  ? 

Emily.  No  doubt  it  is  blackened  by  the  carbon,  which,  when 
its  oxygen  entered  into  combination  with  the  potassium,  was 
deposited  on  its  surface. 

Mrs.  B.  You  are  right.  This  metal  is  perfectly  fluid  at  the 
temperature  of  one  hundred  degrees;  at  fifty  degrees  it  is  solid, 
but  soft  and  malleable ;  at  thirty-two  degrees  it  is  hard  and  brit- 
tle, and  its  fracture  exhibits  an  appearance  of  confused  crystal- 
lization. It  is  scarcely  more  than  half  as  heavy  as  water;  its 
specific  gravity  being  about  six  when  water  is  reckoned  at  ten  ; 
so  that  this  metal  is  actually  lighter  than  any  known  fluid,  even 
than  ether. 

Potassium  combines  with  sulphur  and  phosphorus,  forming 
sulphurets  and  phosphurets  ,  it  likewise  forms  alloys  with  sev- 
erul  metals,  and  amalgamates  with  mercury. 

Emily.  But  can  a  sufficient  quantity  of  potassium  be  obtain- 
ed, by  means  of  the  Voltaic  battery,  to  admit  of  all  its  proper- 
ties and  relations  to  other  bodies  being  satisfactorily  ascertain- 
ed? 

Mrs.  B.  Not  easily ;  but  I  must  not  neglect  to  inform  you 
that  a  method  of  obtaining  this  metal  in  considerable  quanti- 
ties has  since  been  discovered.  Two  eminent  French  chem- 
ists, Thenard  and  Gay  Lussac,  stimulated  by  the  triumph 
which  Sir  H.  Davy  had  obtained,  attempted  to  separate  potas- 
sium from  its  combination  with  oxygen,  by  common  chemical 
means,  and  without  the  aid  of  electricity.  They  caused  red 
hot  potash  in  a  state  of  fusion  to  filter  through  iron  turnings  in 
an  iron  tube,  heated  to  whiteness.  Their  experiment  was 
crowned  with  the  most  complete  success ;  more  potassium  was: 


METALS.  13 

obtained  by  this  single  operation,  than  could  have  been  collect- 
ed in  many  weeks  by  the  most  diligent  use  of  the  Voltaic  bat- 
tery. 

Emily.  In  this  experiment,  I  suppose,  the  oxygen  quitted  its 
combination  with  the  potassium  to  unite  with  the  iron  turnings  ? 

Mrs.  B.  Exactly  so;  and  the  potassium  was  thus  obtained 
in  its  simple  state.  From  that  time  it  has  become  a  most  con- 
venient and  powerful  instrument  of  deoxygenation  in  chemical 
experiments.  This  important  improvement,  engrafted  on  Sir 
II.  Davy's  previous  discoveries,  served  but  to  add  to  his  glory, 
since  the  facts  which  he  had  established,  when  possessed  of  on- 
ly a  few  atoms  of  this  curious  substance,  and  the  accuracy  of 
his  analytical  statements,  were  all  confirmed  when  an  opportu- 
nity occurred  of  repeating  his  experiments  upon  this  substance, 
which  can  now  be  obtained  in  unlimited  quantities. 

Caroline.  What  a  satisfaction  Sir  H  Davy  must  have  felt, 
when  by  an  effort  of  genius  he  succeeded  in  bringing  to  light 
and  actually  giving  existence,  to  these  curious  bodies,  which 
without  him  might  perhaps  have  ever  remained  concealed 
from  our  view ! 

Mrs.  H.  The  next  substance  which  Sir  H.  Davy  submitted 
to  the  influence  of  the  Voltaic  battery  was  Soda,  the  other  fix- 
ed alkali,  which  yielded  to  the  same  powers  of  decomposition  5 
from  this  alkali  too,  a  metallic  substance  was  obtained,  very 
analogous  in  its  properties  to  that  which  had  been  discovered 
in  potash;  Sir  H.  Davy  has  called  it  SODIUM.  It  is  rather 
heavier  than  potassium,  though  considerably  lighter  than  wa- 
ter; it  is  not  so  easily  fusible  as  potassium. 

Encouraged  by  these  extraordinary  results,  Sir  II.  Davy 
next  performed  a  series  of  beautiful  experiments  on  Ammonia^ 
or  the  volatile  alkali,  which,  from  analogy,  he  was  led  to  sus- 
pect might  also  contain  oxygen.  This  he  soon  ascertained  to 
be  the  fact,  but  he  has  not  yet  succeeded  in  obtaining  the  basis 
of  ammonia  in  a  separate  state ;  it  is  from  analogy,  and  from 
the  power  which  the  volatile  alkali  has,  in  its  gaseous  form,  to 
oxydate  iron,  and  also  from  the  amalgams  which  can  i?e  obtain- 
ed from  ammonia  by  various  processes,  that  the  proofs  of  that 
alkali  being  also  a  metallic  oxyd  are  deduced. 

Thus,  then,  the  three  alkalies,  two  of  which  had  always 
been  considered  as  simple  bodies,  have  now  lost  all  claim  to 
that  title,  and  I  have  accordingly  classed  the  alkalies  amongst 
the  compounds,  whose  properties  we  shall  treat  of  in  a  future 
conversation. 

Emily.  What  are  the  other  newly  discovered  metals  which 
you  have  alluded  to  in  your  list  of  simple  bodies? 


1 64  METALS. 

Mrs.  B.  They  are  the  metals  of  the  earths  which  became 
next  the  object  of  Sir  H.  Davy's  researches ;  these  bodies  had 
never  yet  been  decomposed,  though  they  were  strongly  suspect- 
ed not  only  of  being  compounds,  but  of  being  metallic  oxyds. 
From  the  circumstance  of  their  incombustibility  it  was  con- 
jectured, with  some  plausibility,  that  they  might  possibly  be 
bodies  that  had  been  already  burnt. 

Cardine.  And  metals,  when  oxydated,  become,  to  all  ap- 
pearance, a  kind  of  earthy  substance. 

Mrs.  B.  They  have,  besides,  several  features  of  resemblance 
with  metallic  oxyds  ;  Sir  H.  Davy  had  therefore  great  reason 
to  be  sanguine  in  his  expectations  of  decomposing  them,  and  he 
was  not  disappointed.  He  could  not,  however,  succeed  in  ob- 
taining the  basis  of  the  earths  in  a  pure  separate  state ;  but  me- 
tallic alloys  were  formed  with  other  metals,  which  sufficiently 
proved  the  existence  of  the  metallic  basis  of  the  earths. 

The  last  class  of  new  metallic  bodies  which  Sir  H.  Davy 
discovered  was  obtained  from  the  three  undecompounded  acids, 
the  boracic,  the  fluoric,  and  the  muriatic  acids;  but  as  you  are 
entirely  unacquainted  with  these  bodies,  I  shall  reserve  the  ac- 
count of  their  decomposition  till  we  come  to  treat  of  their  prop- 
erties as  acids. 

Thus  in  the  course  of -two  years,  by  the  unparalleled  exer- 
tions of  a  single  individual,  chemical  science  has  assumed  a 
new  aspect.  Bodies  have  been  brought  to  light  which  the  hu- 
man eye  never  before  beheld,  and  which  might  have  remained 
eternally  concealed  under  their  impenetrable  disguise. 

It  is  impossible  at  the  present  period  to  appreciate  to  their 
full  extent  the  consequences  which  science  or  the  arts  may  de- 
rive from  these  discoveries ;  we  may,  however,  anticipate  the 
most  important  results. 

In  chemical  analysis  we  are  now  in  possession  of  more  ener- 
getic agents  of  decomposition  than  were  ever  before  known. 

In  geology  new  views  are  opened,  which  will  probably  ope- 
rate a  revolution  in  that  obscure  and  difficult  science.  It  is  al- 
ready proved  that  all  the  earths,  and,  in  fact,  the  solid  surface 
of  this  globe,  are  metallic  bodies  mineralized  by  oxygen,  and  as 
our  planet  has  been  calculated  to  be  considerably  more  dense 
upon  the  whole  than  it  is  on  the  surface,  it  is  reasonable  to  sup- 
pose that  the  interior  of  the  earth  is  composed  of  a  metallic 
mass,  the  surface  of  which  only  has  been  mineralized  by  the  at- 
mosphere. 

The  eruptions  of  volcanos,  those  stupendous  problems  of  na- 


ON  THE  ATTRACTION  OF  COMPOSITION.        105 

ture,  admit  now  of  an  easy  explanation.*  For  if  the  bowels  of 
the  earth  are  the  grand  recess  of  these  newly  discovered  inflam- 
mable bodies,  whenever  water  penetrates  into  them,  combus- 
tions and  explosions  must  take  place ;  and  it  is  remarkable  that 
the  lava  which  is  thrown  out,  is  the  very  kind  of  substance 
which  might  be  expected  to  result  from  these  combustions. 

I  must  now  take  my  leave  of  you  ;  we  have  had  a  veiy  long 
conversation  to-day,  and  I  hope  you  will  be  able  to  recollect 
what  you  have  learnt.  At  our  next  interview  we  shall  enter  on 
a  new  subject. 


CONVERSATION  XHi. 

ON  THE  ATTRACTION  OF  COMPOSITION. 

Mrs.  B.  HAVING  completed  our  examination  of  the  simple 
or  elementary  bodies,  we  are  now  to  proceed  to  those  of  a 
compound  nature ;  but  before  we  enter  on  this  extensive  sub- 
ject, it  will  be  necessary  to  make  you  acquainted  with  the  prin- 
cipal laws  by  which  chemical  combinations  are  governed. 

You  recollect,  I  hope,  what  we  formerly  said  of  the  nature  of 
the  attraction  of  composition,  or  chemical  attraction,  or  affini- 
ty, as  it  is  also  called  ? 

Emily.  Yes,  I  think,  perfectly ;  it  is  the  attraction  that  sub- 
sists between  bodies  of  a  different  nature,  which  occasions  them 
to  combine  and  form  a  compound,  when  they  come  in  contact, 
and,  according  to  Sir  II.  Davy's  opinion,  this  effect  is  produced 
by  the  attraction  of  the  opposite  electricities,  which  prevail  in 
bodies  of  different  kinds. 

Mrs.  B.  Very  well  ;  your  definition  comprehends  the  first 
law  of  chemical  attraction,  which  is,  that  it  takes  place  only 
between  bodies  of  a  different  nature  ;  as,  for  instance,  between 
an  acid  and  an  alkali ;  between  oxygen  and  a  metal,  &c. 

Caroline.  That  we  understand  of  course ;  for  the  attraction 

*  It  is  always  easy  to  form  a  theory.  But  an  explanation  of  these 
"  stupendous  problems  of  nature,'1  we  believe  has  not  yet  been  de- 
monstrated to  the  satisfaction  of  all.  though  great  learning  and  im- 
mense labor  has  been  bestowed  on  the  subject.  If  the  "  easy  explana- 
tion1' is  founded  on  the  data  here  proposed,  viz.  that  the  solid  surface 
of  our  globe  consists  of  nothing  except  metals  and  oxygen  —such  a 
theory  in  the  present  state  of  knowledge,  must  chiefly  consist  of  suppo- 
sition piled  on  supposition  :  there  being  as  yet  no  proof  that  the  crnst 
of  1h-°  r.arth  is  foioied  only  of  thess  two  elements.  0. 


i66        '  ON    THE     ATTRACTION 

between  particles  of  a  similar  nature  is  that  of  aggregation,,  o» 
cohesion,  which  is  independent  ot'.nnv  ""hf.:iaical  power. 

Mrs.  B.  The  2d  law  of  chemical  attraction  is,  that  it  take's 
place  only  between  the  most  minute  particles  of  bodies  ;  there- 
fore, the  more  you  divide  the  particles  of  the  bodies  to  be  com- 
bined, the  more  readily  they  act  upon  each  other. 

Caroline.  That  is  again  a  circumstance  which  we  might  have 
supposed,  for  the  finer  the  particles  of  the  two  substances  are, 
the  more  easily  and  perfectly  they  will  come  in  i\,uiact  with 
each  other,  which  must  greatly  facilitate  then  union.  It  was 
for  this  purpose,  you  said,  that  you  used  iron  filings,  in  prefer- 
ence to  wires  or  pieces  of  iron,  for  the  decomposition  of  water. 

Airs.  B.  It  was  once  supposed  that  no  mechanical  power 
could  divide  bodies  into  particles  sufficiently  minute  for  them  to 
act  on  each  other  ;  and  that,  in  order  to  produce  the  extreme 
division  requisite  for  a  chemical  action,  one,  if  not  both  of  the 
bodies,  should  be  in  a  fluid  state.  There  are,  however,  a  few 
instances  in  which  two  solid  bodies,  very  finely  pulverized,  ex- 
ert a  chemical  action  on  one  another  ;*  but  such  exceptions  to 
the  general  rule  are  very  rare  indeed. 

Emily.  In  all  the  combinations  that,  we  have  hitherto  seen5 
one  of  the  constituents  has,  I  believe,  been  either  liquid  or 
aeriform.  In  combustions,  for  instance,  the  oxygen  is  taken 
from  the  atmosphere,  in  which  it  existed  in  the  state  of  gas  ; 
and  whenever  we  have  seen  acids  combine  with  metals  or  with 
alkalies,  they  were  either  in  a  liquid  or  an  aeriform  state. 

Mrs.  B  The  3d  law  of  chemical  attraction  is,  that  it  can 
fake  place  between  two,  three,  four,  or  even  a  greater  number 
of  bodies. 

Caroline.  Oxyds  and  aeids  are  bodies  composed  of  two  con- 
stituents $  but  1  recollect  no  instance  of  the  combination  of  a 
greater  number  of  principles. 

Mrs.  B.  The  compound  salts,  formed  by  the  union  of  the 
metals  with  ncids,  are  composed  of  three  principles.  And  thero 
are  salts  formed  by  the  combination  of  the  alkalies  with  the 
Earths  which  are  of  a  similar  d^scriprion. 

Caroline.  Are  they  of  the  same  kind  as  the  metallic  salts  ? 

Mrs.  V.  Yes;  they  are  very  analogous  in  their  nature,  al- 
though different  in  rnanv  of  their  properties. 

A  methodical  nomenclature,  similar  to  that  of  the  acids,  has 
been  adopted  for  the  compound  salts.  Each  individual  salt  de- 
rives its  name  from  its  constituent  parts,  so  thate  very  name  im- 
plies a  knowledge  of  the  composition  of  the  salt. 


']  hi?  j«  the  c^c  )'/i<h  nujriate  of  arr;m  >nia  and  quicklime.     C. 


OF    COMPOSITION.  16? 

'The  three  alkalies,  the  alkaline  earths,  and  the  metals,  are 
called  salifiable  bases  or  radicals ;  and  the  acids,  salifying 
principles.  The  name  of  each  salt  is  composed  both  of  that  of 
the  acid  and  the  salifiable  base;  and  it  terminates  in  at  or  zV, 
according  to  the  degree  of  the  oxygenation  of  the  acid.  Thus, 
for  instance,  all  those  salts  which  are  formed  by  the  combina- 
tion of  the  sulphuric  acid  with  any  of  the  salifiable  bases  are 
nailed  sulphats,  and  the  name  of  the  radical  is  added  for  the 
specific  distinction  of  the  salt ;  if  it  be  potash,  it  will  compose  a 
sulphat  of  potash  ;  if  ammonia,  sulphat  of  ammonia^  &c. 

Emily.  The  crystals  which  we  obtained  from  the  combina- 
tion of  iron  and  sulphuric  acid  were  therefore  sulphat  of  iron  ? 

.\Irs.B.  Precisely;  and  those  which  we  prepared  by  dis- 
solving copper  in  nitric  acid,  nitrat  ofcopper,  and  soon. — But 
this  is  not  all  :  if  the  salt  be  formed  by  that  class  of  acids  which 
ends  in  ous,  (which  you  know  indicates  a  less  degree  of  oxygen- 
ation,) the  termination  of  the  name  of  the  salt  will  be  in  it,  as 
sulphit  of  potash,  sulphit  of  ammonia^  &c. 

Emily.  There  must  be  an  immense  number  of  compound 
salts,  since  there  is  so  great  a  variety  of  salifiable  radicals,  as 
well  as  of  salifying  principles. 

Mrs.  B.  Their  real  number  cannot  be  ascertained,  since  it 
increases  every  day.  But  we  must  not  proceed  further  in  the 
investigation  of  the  compound  salts,  until  we  have  completed 
the  examination  of  the  nature  of  the  ingredients  of  which  they 
are  composed. 

The  4th  law  of  chemical  attraction  is,  that  a  change  of  tem- 
perature always  takes  place  at  the  moment  of  combination. 
This  arises  from  the  extrication  of  the  two  electricities  in  the 
form  of  caloric,  which  always  occurs  when  bodies  unite  ;  and 
also  sometimes  in  part  from  a  change  of  capacity  of  the  bodies 
for  heat,  which  always  takes  place  when  the  combination  is  at- 
tended with  an  increase  of  density,  but  more  especially  when 
the  compound  passes  from  the  liquid  to  the  solid  form.  I  shall 
now  show  you  a  striking  instance  of  a  change  of  temperature 
from  chemical  union,  merely  by  pouring  some  nitrous  acid  on 
this  small  quantity  of  oil  of  turpentine — the  oil  will  instantly 
combine  with  the  oxygen  of  the  acid,  and  produce  a  considera- 
ble change  of  temperature. 

Caroline.  What  a  blaze !  The  temperature  of  the  oil  and 
the  acid  must  be  greatly  raised,  indeed,  to  produce  such  a  vio- 
lent combustion. 

Mrs.  B.  There  is,  however,  a  peculiarity  in  this  combustion, 
which  is,  that  the  oxygen,  instead  of  being  derived  from  the  at- 
mosphere alone,  is  principally  supplied  by  the  acid  itself. 


168  ON    THE    ATTRACTION 

Emily.  And  are  not  all  combustions  instances  of  the  change 
of  temperature  produced  by  the  chemical  combination  of  two 
bodies  ? 

Mrs*  B.  Undoubtedly;  when  oxygen  loses  its  gaseous  form, 
in  order  to  combine  with  a  solid  body,  it  becomes  condensed, 
and  the  caloric  evolved  produces  the  elevation  of  temperature. 
The  specific  gravity  of  bodies  is  at  the  same  time  altered  by 
chemical  combination ;  for  in  consequence  of  a  change  of  capa- 
city for  heat,  a  change  of  density  must  be  produced. 

Caroline.  That  was  the  case  with  the  sulphuric  acid  and  wa- 
ter, which,  by  being  mixed  together,  gave  out  a  great  deal  of 
heat,  and  increased  in  density. 

Mrs.  B.  The  5th  law  of  chemical  attraction  is,  that  the  pro- 
perties lohich  characterise  bodies,  when  separate,  are  altered 
or  destroyed  by  their  combination. 

Caroline.  Certainly  ;  what,  for  instance,  can  be  so  different 
from  water  as  the  hydrogen  and  oxygen  gases  ? 

Emily.  Or  what  more  unlike  sulphat  of  iron  than  iron  01 
sulphuric  acid  ? 

Mrs.  B.  Every  chemical  combination  is  an  illustration  of 
this  rule.  But  let  us  proceed — 

The  6th  law  is,  that  the  force  of  chemical  affinity  between 
the  constituents  of  a  body  is  estimated  by  that  which  is  requir- 
ed for  their  separation.  This  force  is  not  always  proportional 
to  the  facility  with  which  bodies  unite  ;  for  manganese,  for  in- 
stance, which,  you  know,  is  so  much  disposed  to  unite  with  ox- 
ygen that  it  is  never  found  in  a  metallic  state,  yields  it  more 
easily  than  any  other  metal. 

Emily.  But,  Mrs.  B.,  you  speak  of  estimating  the  force  of  at- 
traction between  bodies,  by  the  force  required  to  separate  them ; 
how  can  you  measure  these  forces  ? 

J.TS.  B.  They  cannot  be  precisely  measured,  but  they  are 
comparatively  ascertained  by  experiment,  and  can  be  represent- 
ed by  numbers  which  express  the  relative  degrees  of  attraction. 

The  7th  law  is,  that  bodies  have  amongst  themselves  differ- 
ent degrees  of  attraction.  Upon  this  law,  (which  you  may 
have  discovered  yourselves  long  since,)  the  whole  science  of 
chemistry  depends  ;  for  it  is  by  means  of  the  various  degrees  of 
affinity  which  bodies  have  for  each  other,  that  all  the  chemical 
compositions  and  decompositions  are  effected.  Every  chemic- 
al fact  or  experiment  is  an  instance  of  the  same  kind  ;  and 
whenever  the  decomposition  of  a  body  is  performed  by  the  ad- 
dition of  any  single  new  substance,  it  is  said  to  be  effected  by 
simple  elective  attractions.  But  it  often  happens  that  no  sin> 
pie  substance  will  decompose  a  body,  and  that,  in  order  to  ef~ 


Ot1  COMPOSITION. 


169 


£ecfc  this,  you  must  offer,  to  the  compound  a  body  which  is  itself 
composed  of  two,  or  sometimes  three  principles,  which  would 
not,  each  separately,  perform  the  decomposition.  In  this  case 
there  are  two  new  compounds  formed  in  consequence  of  a  re- 
ciprocal decomposition  and  recomposition.  All  instances  of 
this  kind  are  called  double  elective  attractions. 

Caroline.  I  confess  I  do  not  understand  this  clearly. 

Mrs.  B.  You  will  easily  comprehend  it  by  the  assistance  of 
this  diagram,  in  which  the  reciprocal  forces  of  attraction  are 
represented  by  numbers : 

Original  Compound 
Sulpbat  of  Soda. 


Result 

Nitrat 

ofSoda 


Result 
Sulphat 
of  Lime 


Soda        8  Sulphuric  Acid 

i 


7  Divellent  ^Attractions  6-13 

I 

Nitric  Acid  4  Lime 

• 

12 

*^*  V~  '  "*-'' 

Original  Compound 
ISitrat  of  Lime. 


We  here  suppose  that  we  are  to  decompose  sulphat  of  soda ; 
that  is,  to  separate  the  acid  from  the  alkali ;  if,  for  this  purpose 
we  add  some  lime,  in  order  to  make  it  combine  with  the  acid, 
we  shall  fail  in  our  attempt,  because  the  soda  and  the  sulphuric 
acid  attract  each  other  by  a  torce  which  is  superior,  and  (by 
way  of  supposition)  is  represented  by  the  number  8  ;  while  the 
lime  tends  to  unite  with  this  arid  by  an  affinity  equal  only  to 
the  number  6.  It  is  plain,  therefore,  that  the  sulphat  of  soda 
will  not  be  decomposed,  since  a  force  equal  to  8  cannot  be  over- 
come by  a  force  equal  only  to  6. 

Caroline.  So  far.  this  appears  very  clear. 

Mrs.  B.  If,  on  the  other  hand,  we  eadeayour  to  decompose 
16 


170  ON   THE   ATTRACTION 

this  salt  by  nitric  acid,  which  tends  to  combine  with  soda,  we 
shall  be  equally  unsuccessful,  as  nitric  acid  tends  to  unite  with 
the  alkali  by  a  force  equal  only  to  7- 

In  neither  of  these  cases  of  simple  elective  attraction,  there- 
fore, can  we  accomplish  our  purpose.  But  let  us  previously 
combine  together  the  lime  and  nitric  acid,  so  as  to  form  a  nitrat 
of  lime,  a  compound  salt,  the  constituents  of  which  are  united  by 
a  power  equal  to  4.  If  then  we  present  this  compound  to  the 
sulphat  of  soda,  a  decomposition  will  ensue,  because  the  sum  of 
the  forces  which  tend  to  preserve  the  two  salts  in  their  actual 
state  is  not  equal  to  that  of  the  forces  which  tend  to  decompose 
them,  and  to  form  new  combinations.  The  nitric  acid,  there- 
fore, will  combine  with  the  soda,  and  the  sulphuric  acid  with 
the  lime.* 

Caroline.  I  understand  you  now  very  well.  This  double  ef- 
fect takes  place  because  the  numbers  8  and  4,  which  represent 
the  degrees  of  attraction  of  the  constituents  of  the  two  original 
salts,  make  a  sum  less  than  the  numbers  7  and  6,  which  repre- 
sent the  degrees  of  attraction  of  the  two  new  compounds  that 
will  in  consequence  be  formed. 

Mrs.  B.  Precisely  so. 

Caroline.  But  what  is  the  meaning  of  quiescent  and  divel- 
lent  forces,  which  are  written  in  the  diagram  ? 

Mrs.  B.  Quiescent  forces  are  those  which  tend  to  preserve 
compounds  in  a  state  of  rest,  or  such  as  they  actually  are  :  di- 
vellent  forces,  those  which  tend  to  destroy  that  state  of  combi- 
nation, and  to  form  new  cdmpounds. 

These  are  the  principal  circumstances  relative  to  the  doctrine 
of  chemical  attractions,  which  have  been  laid  down  as  rules  by 
modern  chemists ;  a  few  others  might  be  mentioned  respecting 
the  same  theory,  but  of  less  importance,  and  such  as  would 
take  us  too  far  from  our  plan.  I  should,  however,  not  omit  to 
mention  that  Mr.  Berthollet,  a  celebrated  Fremch  chemist,  has 
questioned  the  uniform  operation  of  elective  attraction,  and  has 
advanced  the  opinion,  that,  in  chemical  combinations,  the  chan- 
ges which  take  place  depend  not  only  upon  the  affinities,  but 

*  Suppose  we  say  thus.  The  sulphuric  acid  attracts  soda  with  a 
stronger  force  than  it  does  /me,  andsorfa  has  a  stionger  affinity  foi  sul- 
phuric acid  than  it  has  for  nitric  acid.  It  is  plain  then,  that  neither 
lime  nor  nitric  acid  alone  will  decompose  the  sulphat  ofr  soda.  Now 
if  we  unite  the  nitric  acid  and  lime,  we  form  nitrate  of  lime.  But  the 
nitric  acid  has  not  so  strong  an  affinity  for  the  lime  as  it  has  for  soda. 
On  mixing  the  two  salts  in  solution,  therefore,  the  nitric  acid  quits  the 
lime,  and  combines  with  the  soda.  This  leaves  the  sulphuric  acid  and 
the  lime  free  and  uncombined ;  they  then  unite  and  form  sulphat  o* 
lime.  C. 


OP  COMPOSITION.  171 

also,  in  some  degree,  on  the  respective  quantities  of  the  substan- 
ces concerned,  on  the  heat  applied  during  the  process,  and 
some  other  circumstances. 

Caroline.  In  that  case,  I  suppose,  there  would  hardly  be 
two  compounds  exactly  similar,  though  composed  of  the  same 
materials  ? 

Mrs.  B.  On  the  contrary,  it  is  found  that  a  remarkable  uni- 
formity prevails,  as  to  proportions,  between  the  ingredients  of 
bodies  of  similar  composition.  Thus  water,  as  you  may  re- 
collect to  have  seen  in  a  former  conversation,  is  composed  of 
two  volumes  of  hydrogen  gas  to  one  of  oxygen,  and  this  is  al- 
ways found  to  be  precisely  the  proportion  of  its  conitituents, 
from  whatever  source  the  water  be  derived.  The  same  uni- 
formity prevails  with  regard  to  the  various  salts  5  the  acid  and 
alkali,  in  each  kind  of  salt,  being  always  found  to  combine  in 
the  same  proportion.  Sometimes,  it  is  true,  the  same  acid,  and 
the  same  alkali  are  capable  of  making  two  distinct  kinds  of 
salts  ;  but  in  all  these  cases  it  is  found  that  one  of  the  salts  con- 
tains just  twice,  or  in  some  instances,  thrice  as  much  acid,  or 
alkali,  as  the  other.* 

Emily.  If  the  proportions  in  which  bodies  combine  are  so 
constant  and  so  well  defined,  how  can  Mr.  Berthollet's  remark 
be  reconciled  with  this  uniform  system  of  combination  ? 

Mrs.  B.  Great  as  that  philosopher's  authority  is  in  chemis- 
try, it  is  now  generally  supposed  that  his  doubts  on  this  subject 
were  in  a  great  degree  groundless,  and  that  the  exceptions  he 

*  The  student  already  understands,  that  in  chemical  combinations 
the  union  takes  place  only  between  the  particles,  or  atoms,  of  substan- 
ces. These  atoms,  it  is  supposed  are  indivisible,  being  the  ultimate 
particles  of  which  bodies  are  composed.  In  chemical  combinations, 
then,  where  substances  are  capable  of  uniting  in  only  one  proportion, 
this  must  be  atom  to  atom.  Thus  oxygen  and  hydrogen  unite  only  in 
the  proportions  of  100  of  the  former  to  750  of  the  latter  by  weight, 
Here  an  atom  of  oxygen  unites  to  an  atom  of  hydrogen  to  form  water ; 
but  the  atoms  of  oxygen  are  seven  and  an  half  times  heavier  than  those 
of  hydrogen. 

When  substances  unite  in  several  proportions,  the  second  and  third 
are  always  multiples  of  the  first.  Thus  100  parts  of  manganese,  will 
unite  to  14,  28,  42,  or  56  of  oxygen,  but  not  with  any  intermediate 
quantity,  as  with  12,  20,  60,  &c.  This  la\r  of  definite  proportions, 
so  far  as  is  known,  holds  good,  where  the  resulting  compound  differs 
widely  from  either  of  the  substances  of  which  it  is  composed,  as  in  the 
salts,  compound  minerals,  &c.  The  theory  of  definite  proportions  is 
explained  by  supposing  that  a  substance  which,  we  shall  call  A,  unites 
with  another  substance  B,  atom  to  atom,  and  that  this  forms  a  certain 
compound.  When  they  unite  in  the  second  proportion,  two  atoms  of 
B  unite  to  one  of  A,  and  this  forms  another  compound,  and  so  on,  un» 
til  the  atoms  of  A  can  unite  to  no  more  of  B.  C. 


172  ON  THE  ATTRACTION  OP  COMPOSITION. 

has  observed  in  the  laws  of  definite  proportions,  have  been  on- 
ly appaient,  and  may  be  accounted  for  consistently  with  those 
laws. 

Caroline.  Pray,  Mrs.   B.,   can  you  decompose  a  salt   by 

means  of  electricity,  in  the  same  way  as  we  decompose  water? 

JWrs.  Li.  Undoubtedly  ;  and  I  am  glad  this  question  occurred 

to  you,  because  it  gives  me  an  opportunity   of  showing  you 

some  very  interesting  experiments  on  the  subject. 

If  we  dissolve  a  quantity,  however  small,  of  any  salt  in  a 
glass  of  water,  and  if  we  plunge  into  it  the  extremities  of  the 
wires  which  proceed  from  the  two  ends  of  the  Voltaic  battery, 
the  salt  will  be  gradually  decomposed,  the  acid  being  attracted 
by  the  positive,  and  the  alkali  by  the  negative  wire. 

Emily.  But  how  can  you  render  that  decomposition  per- 
ceptible  ? 

Mrs.  B.  By  placing  in  contact  with  the  extremities  of  each 
Wire,  in  the  solution,  pieces  of  paper  stained  with  certain  veget- 
able colours,  which  are  altered  by  the  contact  of  an  acid  or  an 
alkali.  Thus  this  blue  vegetable  preparation  called  litmus  be- 
comes red  when  touched  by  an  acid  ;  and  the  juice  of  violets 
becomes  green  by  the  contact  of  an  alkali. 

But  the  experiment  can  be  made  in  a  much  more  distinct 
manner,  by  receiving  the  extremities  of  the  wires  into  two  dif- 
ferent vessels,  so  that  the  alkali  shall  appear  in  one  vessel  and 
the  acid  in  the  other. 

Caroline.  But  then  the  Voltaic  circle  will  not  be  completed  j 
how  can  any  effect  be  produced  ? 

Mrs.  B.  You  are  right  ;  I  ought  to  have  added  that  the  two 
vessels  must  be  connected  together  by  some  interposed  sub- 
stance capable  of  conducting  electricity.  A  piece  of  moistened 
cotton-wick  answers  this  purpose  very  well.  You  see  that  the 
cotton  (PLATE  XIII.  fig.  2.  c.)  has  one  end  immersed  in  one 
glass  and  the  other  end  in  the  other,  so  as  to  establish  a  com- 
munication between  any  fluids  contained  in  them.  We  shall 
now  put  into  each  of  the  glasses  a  little  glauber  salt,  or  sulphat 
of  soda,  (which  consists  of  an  acid  and  an  alkali,)  and  then 
we  shall  fill  the  glasses  with  water,  which  will  dissolve  the  salt. 
Let  us  now  connect  the  glasses  by  means  of  the  wires  (e,  d,) 
with  the  two  ends  of  the  battery,  thus  .... 

Caroline.  The  wires  are  already  giving  out  small  bubbles ; 
is  this  owing  to  the  decomposition  of  salt  ? 

Mrs.  B.  No  ;  these  are  bubbles  produced  by  the  decompo- 
sition of  the  water,  as  you  saw  in  a  former  experiment.  In  or- 
der to  render  the  separation  of  the  acid  from  the  alkali  visible, 
I  pour  into  the  glass  (a.)  which  is  connected  with  the  positive 


J.  Titrate  Battery  of*  iinprvt'fd  ccmtirtcfton  vith  tht  Ptates  otif  oft&c  Cels- 
3  SO  'tin* fences  df  tfiam'ral  ttecvntpofitien  3>\"  tfie  Teltaic  Jtaffery. 


ALKALIES.  173 

wire,  a  few  drops  of  a  solution  of  litmus,  which  the  least  quan- 
tity of  acid  turns  red  ;  and  in  the  other  glass  (b,)  which  is  con- 
nected with  the  negative  wire,  I  pour  a  few  drops  of  the  juice 
of  violets  .... 

Emily.  The  blue  solution  is  already  turning  red  all  round 
the  wire. 

Caroline.  And  the  violet  solution  is  beginning  to  turn  green. 
This  is  indeed  very  singular  ! 

Mrs.  B.  You  will  be  still  more  astonished  when  we  vary  the 
experiment  in  this  manner  : — These  three  glasses  (fig.  3.  f,  g, 
h,)  are,  as  in  the  former  instance,  connected  together  by  wetted 
cotton,  but  the  middle  one  alone  contains  a  saline  solution,  the 
two  others  containing  only  distilled  water,  coloured  as  before 
by  vegetable  infusions.  Yet,  on  making  the  connection  with 
the  battery,  the  alkali  will  appear  in  the  negative  glass  (h,)  and 
the  acid  in  the  positive  glass  (f,)  though  neither  of  them  con- 
tained anly  saline  matter. 

Emily.  So  that  the  acid  and  the  alkali  must  be  conveyed 
right  and  left  from  the  central  glass,  into  the  other  glasses,  by 
means  of  the  connecting  moistened  cotton  ? 

Mrs.  B.  Exactly  so ;  and  you  may  render  the  experiment 
still  more  striking,  by  putting  into  the  central  glass  (k,  fig.  4.) 
an  alkaline  solution,  the  glauber  salt  being  placed  into  the  nega- 
tive glass  (1,)  and  the  positive  glass  (i)  containing  only  water. 
The  acid  will  be  attracted  by  the  positive  wire  (m,)  and  will 
actually  appear  in  the  vessel  (i,)  after  passing  through  the  alka- 
line solution  (k,)  without  combining  with  it,  although,  you 
know,  acids  and  alkalies  are  so  much  disposed  to  combine. — 
But  this  conversation  has  already  much  exceeded  our  usual 
limits,  and  we  cannot  enlarge  more  upon  this  interesting  sub- 
feet  at  present. 


CONVERSATION  XIV. 

ON  ALKALIES. 

Mrs,  B.  HAVING  now  given  you  some  idea  of  the  laws  by 
•which  chemical  attractions  are  governed,  we  may  proceed  to 
the  examination  of  bodies  which  are  formed  in  consequence  of 
these  attractions. 

The  first  class  of  compounds  that  present  themseVes  to  our 
notice,  in  our  gradual  ascent  to  the  most  complicated  combina- 
tions, are  bodies  composed  of  only  two  principles.  The  sul- 


174  ALKALIES, 

phurets,  phosphurets,  carburets,  &c.  are  of  this  description  ; 
but  the  most  numerous  and  important  of  these  compounds  are 
the  combination  of  oxygen  with  the  various  simple  substances 
with  which  it  has  a  tendency  to  unite.  Of  these  you  have  al- 
ready acquired  some  knowledge,  but  it  will  be  necessary  to  en- 
ter into  further  particulars  respecting  the  nature  and  properties 
of  those  most  deserving  our  notice.  Of  this  class  are  the  AL- 
KALKS  and  the  EARTHS,  which  we  shall  successively  examine. 

We  shall  first  take  a  view  of  the  alkalies,  of  which  there  are 
three,  viz.  POTASH,  SODA,  and  AMMONIA.  The  two  first  are 
called  Jixed  alkalies,*  because  they  exist  in  a  solid  form  at  the 
temperature  of  the  atmosphere,  and  require  a  great  heat  to  be 
volatilised.  They  consist,  as  you  already  know,  of  metallic 
bases  combined  with  oxygen.  In  potash,  the  proportions  are 
about  eighty-six  parts  of  potassium  to  fourteen  of  oxygen  ;  and 
in  soda,  seventy-seven  parts  of  sodium  to  twenty-three  of  oxy- 
gen. The  third  alkali,  ammonia,  has  been  distinguished  by 
the  name  of  volatile  alkali,  because  its  natural  form  is  that  of 
gas.  Its  composition  is  of  a  more  complicated  nature,  of  which 
we  shall  speak  hereafter. 

Some  of  the  earths  bear  so  strong  a  resemblance  in  their 
properties  to  the  alkalies,  that  it  is  difficult  to  know  under  which 
head  to  place  them.  The  celebrated  French  chemist,  Four- 
sroy,  had  classed  two  of  them  (barytes  and  strontites)  with  the 
alkalies;  but  as  lime  and  magnesia  have  almost  an  equal  title  to 
that  rank,  I  think  it  better  not  to  separate  them,  and  therefore 
have  adopted  the  common  method  of  classing  them  with  the 
earths,  and  of  distinguishing  them  by  the  name  of  alkaline 
earths. 

The  general  properties  of  alkalies  are,  an  acrid  burning 
taste,  a  pungent  smell,  and  a  caustic  action  on  the  sk  n  and  flesh  j 

Caroline.  I  wonder  that  they  should  be  caustic,  Mrs.  B.,' 
since  they  contain  so  little  oxygen. 

Mrs.  B.  Whatever  substance  has  an  affinity  for  any  one  of 
the  constituents  of  animal  matter,  sufficiently  powerful  to  de- 
compose it,  is  entitled  to  the  appellation  of  caustic.  The  alka- 
lies, in  their  pure  state,  have  a  very  strong  attraction  for  water, 
for  hydrogtn,  and  for  carbon,  which,  you  know,  are  the  con- 

*  It  has  already  been  stated  that  a  third  fixed  alkali  has  lately  been 
discovered  by  Mr.  Aifoiedson,  which  has  been  called  lilhion.  It 
was  first  found  in  a  Swedish  mineral  called  petalite ;  but  has  since 
teen  detected  in  some  other  miners'?.  Though  this  alkali  resembles 
potash  and  soda  in  its  general  properties,  yet  it  is  decidedly  an  alka- 
linp  substance  01  its  own,  capable  of  forming  different  salts  with  the 
acids,  and  having  in  particular  the  property  of  combining  with 
greater  proportions  of  acid  than  the  other  alkalies. 


POTASH.  If5 

stituent  principles  of  oil,  and  it  is  chiefly  by  absorbing  these 
substances  from  animal  matter  that  they  effect  its  decomposi- 
tion ;  for,  when  diluted  with  a  sufficient  quantity  of  water,  or 
combined  with  any  oily  substance,  they  lose  their  causticity. 

But,  to  return  to  the  general  properties  of  alkalies — they 
change,  as  we  have  already  seen,  the  colour  of  syrup  of  vio- 
lets, and  other  blue  vegetable  infusions,  to  green  ;  and  have, 
in  general,  a  very  great  tendency  to  unite  with  acids,  although 
the  respective  qualities  of  these  two  classes  of  bodies  form  a 
remarkable  contrast. 

We  shall  examine  the  result  of  the  combination  of  acids  and 
alkalies  more  particularly  hereafter.  It  will  be  sufficient  at 
present  to  inform  you,  that  whenever  acids  are  brought  in  con- 
tact with  alkalies,  or  alkaline  earths,  they  unite  with  a  remark- 
able eagerness,  and  form  compounds  perfectly  different  from 
either  of  their  constituents  5  these  bodies  are  called  neutral  or 
eompound  salts. 

The  dry  white  powder  which  you  see  in  this  phial  is  pure 
caustic  POTASH;  it  is  very  difficult  to  preserve  it  in  this  state,  as 
it  attracts,  with  extreme  avidity,  the  moisture  from  the  atmos- 
phere, and  if  the  air  were  not  perfectly  excluded,  it  would,  in  a 
very  short  time,  be  actually  melted. 

Emily.  It  is  then,  I  suppose,  always  found  in  a  liquid  state? 

Mrs.  B.  No ;  it  exists  in  nature  in  a  great  variety  of  forms 
and  combinations,  but  is  never  found  in  its  pure  separate  state  5 
it  is  combined  with  carbonic  acid,  with  which  it  exists  in  every 
part  of  the  vegetable  kingdom,  and  is  most  commonly  obtained 
from  the  ashes  of  vegetables,  which  are  the  residue  that  remains 
after  all  the  other  parts  have  been  volatilised  by  combustion. 

Caroline.  But  you  once  said,  that  after  all  the  volatile  parts 
of  a  vegetable  were  evaporated,  the  substance  that  remained 
was  charcoal  ? 

Mrs.  B.  I  am  surprised  that  you  should  still  confound  the 
processes  of  volatilisation  and  combustion.  In  order  to  pro- 
cure charcoal,  we  evaporate  such  parts  as  can  be  reduced  to  va- 
pour by  the  operation  of  heat  alone ;  but  when  we  burn  the 
vegetable,  we  burn  the  carbon  also,  and  convert  it  into  carbonic 
acid  gas. 

Caroline.  That  is  true ;  I  hope  I  shall  make  no  more  mis- 
takes in  my  favourite  theory  of  combustion. 

Mrs.  B.  Potash  derives  its  name  from  the  pots  in  which  the 
vegetables,  from  which  it  was  obtained,  used  formerly  to  be 
burnt ;  the  alkali  remained  mixed  with  the  ashes  at  the  bot- 
tom, and  was  thence  called  potash. 

Emily.  The  ashes  of  a  wood-fire,  then,  are  potash,  since 
they  are  vegetable  ashes  ? 


17  POTASH. 

Mrs.  B.  They  always  contain  more  or  less  potash,  but  are 
very  far  from  consisting  of  that  substance  alone,  as  they  are  a 
mixture  of  various  earths  and  salts  which  remain  after  the  com- 
bustion of  vegetables,  and  from  which  it  is  not  easy  to  separate 
the  alkali  in  its  pure  form.  The  process  by  which  potash  is 
obtained,  even  in  the  imperfect  state  in  which  it  is  used  in  the 
arts,  is  much  more  complicated  than  simple  combustion .  It 
•was  once  deemed  impossible  to  separate  it  entirely  from  all  for- 
eign substances,  and  it  is  only  in  chemical  laboratories  that  it 
is  to  be  met  with  in  the  state  of  purity  in  which  you  find  it  in 
this  phial.  Wood-ashes  are,  however,  valuable  for  the  alkali 
which  they  contain,  and  are  used  for  some  purposes  without 
any  further  preparation.  Purified  in  a  certain  degree,  they 
make  what  is  commonly  called  pearl-ash,  which  is  of  great  ef- 
ficacy in  taking  out  grease,  in  washing  linen,  &c. ;  for  potash 
combines  readily  with  oil  or  fat,  with  which  it  forms  a  com- 
pound well  known  to  you  under  the  name  of  soap. 

Caroline.  Really !  Then  I  should  think  it  would  be  better 
to  wash  all  linen  with  pearl-ash  than  with  soap,  as,  in  the  latter 
case,  the  alkali  being  already  combined  with  oil,  must  be  less 
efficacious  in  extracting  grease. 

Mrs.  R.  Its  effect  would  be  too  powerful  on  fine  linen,  and 
v/ould  injure  its  texture ;  pearl-ash  is  therefore  only  used  for 
that  which  is  of  a  strong  coarse  kind.  For  the  same  reason 
you  cannot  wash  your  hands  with  plain  potash ;  but,  when 
mixed  with  oil  in  the  form  of  soap,  it  is  soft  as  well  as  cleansing, 
and  is  therefore  much  better  adapted  to  the  purpose. 

Caustic  potash,  as  we  already  observed,  acts  on  the  skin, and 
animal  fibre,  in  virtue  of  its  attraction  for  water  and  oil,  and 
converts  all  animal  matter  into  a  kind  of  saponaceous  jelly. 

Emily.  Are  vegetables  the  only  source  from  which  potash 
can  be  derived  ? 

Mrs.  B.  No :  for  though  far  most  abundant  in  vegetables,  it 
is  by  no  means  confined  to  that  class  of  bodies,  being  found  al- 
so on  the  surface  of  the  earth,  mixed  with  various  minerals,  es- 
pecially with  earths  and  stones,  whence  it  is  supposed  to  be 
conveyed  into  vegetables  by  the  roots  of  the  plant.  It  is  also 
met  with,  though  in  very  small  quantities,  in  some  animal  sub- 
stances. The  most  common  state  of  potash  is  that  of  carbo' 
not  y  I  suppose  you  understand  what  that  is  ? 

Emily.  I  believe  so  ;  though  I  do  not  recollect  that  you  ever 
mentioned  the  word  before.  If  I  am  not  mistaken,  it  must  be 
a  compound  salt,  formed  by  the  union  of  carbonic  acid  with 
potash. 

Mrs.  B.  Very  true  j  you  see  bow  admirably  the  nomencla- 


POTASH.  177 

ture  of  modern  chemistry  is  adapted  to  assist  the  memory  5 
when  you  hear  the  name  of  a  compound,  you  necessarily  learn 
what  are  its  constituent  parts;  and  when  you  arc  acquainted 
with  these  constituents,  you  can  immediately  name  the  com- 
pound which  they  form. 

Caroline.  Pray,  how  were  bodies  arranged  and  distinguish- 
ed before  this  nomenclature  was  introduced  ? 

Mrs.  B.  Chemistry  was  then  a  much  more  difficult  study ; 
for  every  substance  had  an  arbitrary  name,  which  it  derived 
either  from  the  person  who  discovered  it,  as  Glauber's  salts 
for  instance;  or  from  some  other  circumstance  relative  to  it, 
though  quite  unconnected  with  its  real  nature,  as  potash. 

These  names  have  been  retained  for  some  of  the  single  bod- 
ies; for  as  this  class  is  not  numerous,  and  therefore  can  easily 
be  remembered,  it  has  not  been  thought  necessary  to  change 
them. 

Emily.  Yet  I  think  it  would  have  rendered  the  new  nomen- 
clature more  complete  to  have  methodised  the  names  of  th<.  1- 
ementary,  as  well  as  of  the  compound  bodies,  though  it  could 
not  have  been  done  in  the  same  manner.  But  the  names  of  the 
simple  substances  might  have  indicated  their  nature,  or,  at  least, 
some  of  their  principal  properties  ;  and  if,  like  the  acids  and 
compound  salts,  all  the  simple  bodies  had  a  similar  termination, 
they  would  have  been  immediately  known  as  such.  So  com- 
plete and  regular  a  nomenclature  would,  I  think,  have  given  a 
clearer  and  more  comprehensive  view  of  chemistry  than  the 
present,  which  is  a  medley  of  the  old  and  new  terms. 

Mrs.  B.  But  you  are  not  aware  of  the  difficulty  of  introduc- 
ing into  science  an  entire  set  of  new  terms  ;  it  obliges  all  the 
teachers  and  professors  to  go  to  school  again,  and  if  some  of  the 
old  names,  that  are  least  exceptionable,  were  not  left  as  an  in- 
troduction to  the  new  ones,  few  people  would  have  had  indus- 
try and  perseverance  enough  to  submit  to  the  study  of  a  com- 
pletely new  language;  and  the  inferior  classes  of  artists,  who 
can  only  act  from  habit  and  routine,  would,  at  least  for  a  time, 
have  felt  material  inconvenience  from  a  total  change  of  their 
habitual  terms.  From  these  considerations,  Lavoisier  and  his 
colleagues,  who  invented  the  new  nomenclature,  thought  it  most 
prudent  to  leave  a  few  links  of  the  old  chain,  in  order  to  con- 
nect it  with  the  new  one.  Besides,  you  may  easily  conceive 
the  inconvenience  which  might  arise  from  giving  a  regular  nom- 
enclature to  substances,  the  simple  nature  of  which  is  always 
uncertain ;  for  the  new  names  might,  perhaps,  have  proved  to 
have  been  founded  in  error.  And,  indeed,  cautious  as  the  in- 
ventors of  the  modern  chemical  language  have  been,  it  has  al- 


178  POTASH. 

ready  been  found  necessary  to  modify  it  in  many  respects.  Iu 
those  few  cases,  however,  in  which  new  terms  have  been  adopt- 
ed to  designate  simple  bodies,  these  names  have  been  so  con- 
trived as  to  indicate  one  of  the  chief  properties  of  the  body  in 
question  ;  this  is  the  case  with  oxygen,  which,  as  1  explained 
to  you,  signifies  generator  of  acids  ;  and  hydrogen  generator  of 
water.  If  all  the  elementary  bodies  had  a  similar  termination, 
as  you  propose,  it  would  be  necessary  to  change  the  name  of 
any  that  might  hereafter  be  found  of  a  compound  nature,  which 
would  be  very  inconvenient  in  this  age  of  discovery. 

But  to  return  to  the  alkalies. — We  shall  now  try  to  melt 
some  of  this  caustic  potash  in  a  little  water,  as  a  circumstance 
occurs  during  its  solution  very  worthy  of  observation. — Do  you 
feel  the  heat  that  is  produced  ? 

Caroline.  Yes,  I  do ;  but  is  not  this  directly  contrary  to  our 
theory  of  latent  heat,  according  to  which  heat  is  disengaged 
when  fluids  become  solid,  and  cold  produced  when  solids  are 
melted. 

Mrs.  B.  The  latter  is  really  the  case  in  all  solutions  ;  and  if 
the  solution  of  caustic  alkalies  seems  to  make  an  exception  to 
the  rule,  it  does  not,  1  believe,  form  any  solid  objection  to  the 
theory.  The  matter  may  be  explained  thus :  When  water  first 
comes  in  contact  with  the  potash,  it  produces  an  effect  similar 
to  the  slaking  of  lime,  that  is,  the  water  is  solidified  in  combi- 
ning with  the  potash,  and  thus  loses  its  latent  heat ;  this  is  the 
lieat  that  you  now  feel,  and  which  is,  therefore,  produced  not 
by  the  melting  of  the  solid,  but  by  the  solidification  of  the  fluid. 
But  when  there  is  more  water  than  the  potash  can  absorb  and 
solidify,  the  latter  then  yields  to  the  solvent  power  of  the  wa- 
ter ;  and  if  we  do  not  perceive  the  cold  produced  by  its  melting, 
it  is  because  it  is  counterbalanced  by  the  heat  previously  dis- 
engaged.* 

A  very  remarkable  property  of  potash  is  the  formation  of 
glass  by  its  fusion  with  siliceous  earth.  You  are  not  yet  ac- 
quainted with  this  last  substance,  further  than  its  being  in  the 
list  of  simple  bodies.  It  is  sufficient  for  the  present,  that  you 
should  know  that  sand  and  flint  are  chiefly  composed  of  it; 
alone,  it  is  infusible,  but  mixed  with  potash,  it  melts  when  ex- 
posed to  the  heat  of  a  furnace,  combines  with  the  alkali,  and 
runs  into  glass. 

Caroline.  Who  would  ever  have  supposed  that  the  same  sub- 

*  This  defence  of  the  general  theory,  however  plausible,  is  liable  to 
some  obvious  objections.  The  phenomenon  might  perhaps  be  better 
accounted  for  by  supposing  that  a  solution  of  alkali  in  water  has  less 
capacity  for  heat  than  either  water  or  alkali  in  their  separate  state. 


POTASH.  179 

stance  which  converts  transparent  oil  into  such  an  opaque  body 
as  50-tp,  should  transform  that  opaque  substance,  sand,  into 
transparent  glass ! 

Mrs.  B.  The  transparency,  or  opacity  of  bodies,  does  not,  I 
conceive,  depend  so  much  upon  their  intimate  nature,  as  upon 
the  arrangement  of  their  particles:  we  cannot  have  a  more 
striking  instance  of  this,  than  is  afforded  by  the  different  states 
of  carbon,  which,  though  it  commonly  appears  in  the  form  of  a 
black  opaque  body,  sometimes  assumes  the  most  dazzling  trans- 
parent form  in  nature,  that  of  diamond,  which,  you  recollect,  is 
carbon,  and  which,  in  all  probability,  derives  its  beautiful  trans- 
parency from  the  peculiar  arrangement  of  its  particles  during 
their  crystallisation. 

Emily.  I  never  should  have  supposed  that  the  formation  of 
glass  was  so  simple  a  process  as  you  describe  it. 

Mrs.  B.  It  is  by  no  means  an  easy  operation  to  make  perfect 
glass  ;  for  if  the  sand  or  flint,  from  which  the  siliceous  earth  is 
obtained,  be  mixed  with  any  metallic  particles,  or  other  sub- 
stance, which  cannot  be  vitrified,  the  glass  will  be  discoloured, 
or  defaced,  by  opaque  specks. 

Caroline.  That,  I  suppose,  is  the  reason  why  objects  so  of- 
ten appear  irregular  and  distorted  through  a  common  glass- 
window. 

Mrs.  B.  This  species  of  imperfection  proceeds,  I  believe, 
from  another  cause.  It  is  extremely  difficult  to  prevent  the 
lower  part  of  the  vessels,  in  which  the  materials  of  glass  are 
fused,  from  containing  a  more  dense  vitreous  matter  than  the 
upper,  on  account  of  the  heavier  ingredients  falling  to  the  bot- 
tom. When  this  happens,  it  occasions  the  appearance  of  veins 
or  waves  in  the  glass,  from  the  difference  of  density  in  its  seve- 
ral parts,  which  produces  an  irregular  retraction  of  the  rays  of 
Light  which  pass  through  it. 

Another  species  of  imperfection  sometimes  arises  from  the 
fusion  not  being  continued  for  a  length  of  time  sufficient  to  com- 
bine the  two  ingredients  completely,  or  from  the  due  propor- 
tion of  potash  and  silex  (which  are  as  two  to  one)  not  being 
carefully  observed;  the  glass,  in  those  cases,  will  be  liable  to 
alteration  from  the  action  of  the  air,  of  salts,  and  especially  of 
acids,  which  will  effect  its  decomposition  by  combining  with 
the  potash,  and  forming  compound  salts. 

Emily.  What  an  extremely  useful  substance  potash  is  ! 

Mrs.  B.  Besides  the  great  importance  of  potash  in  the  man- 
ufactures of  glass  and  soap,  it  is  of  very  considerable  utility  in 
many  of  the  other  arts,  and  in  its  combinations  with  several 
particularly  the  nitric,  with  which  it  forms  saltpetre. 


180  SODA. 

Caroline.  Then  saltpetre  must  be  a  nitrat  of  potash  ?  But 
we  are  not  yet  acquainted  with  the  nitric  acid  ? 

Mrs.  K.  We  shall  therefore  defer  entering  into  the  particu- 
lars of  these  combinations  till  we  come  to  a  general  review  of 
the  compound  salts.  In  order  to  avoid  confusion,  it  will  be  bet- 
ter at  present  to  confine  ourselves  to  the  alkalies. 

Emily.  Cannot  you  show  us  the  change  of  colour  which  you 
said  the  alkalies  produced  on  blue  vegetable  infusions  ? 

Mrs.  B.  Yes,  very  easily.  I  shall  dip  a  piece  of  white  pa- 
per into  this  syrup  of  violets,  which,  you  see,  is  of  a  deep  blue, 
and  dyes  the  paper  of  the  same  colour. — As  soon  as  it  is  dry, 
we  shall  dip  it  into  a  solution  of  potash,  which,  though  itself 
colourless,  will  turn  the  paper  green — * 

Caroline.  So  it  has,  indeed  !  And  do  the  other  alkalies  pro- 
duce a  similar  effect  ? 

Mrs.  B.  Exactly  the  same. — We  may  now  proceed  to  SODA, 
which,  however  important,  will  detain  us  but  a  very  short  time  ; 
as  in  all  its  general  properties  it  very  strongly  resembles  pot- 
ash ;  indeed,  so  great  is  their  similitude,  that  they  have  been 
long  confounded,  and  they  can  now  scarcely  be  distinguished, 
except  by  the  difference  of  the  salts  which  they  form  with  acids. 
The  great  source  of  this  alkali  is  the  sea,  where,  combined 
with  a  peculiar  acid,  it  forms  the  salt  with  which  the  waters  of 
the  ocean  are  so  strongly  impregnated. 

Emily.  Is  not  that  the  common  table  salt  ? 
Mrs.  B.  The  very  same  ;  but  again  we  must  postpone  en- 
tering into  the  particulars  of  this  interesting  combination,  till 
we  treat  of  the  neutral  salts.    Soda  may  be  obtained  from  com- 
mon salt ;  but  the  easiest  and  most  usual  method  of  procuring 
it  is  by  the  combustion  of  marine  plants,  an  operation  perfectly 
analogous  to  that  by  which  potash  is  obtained  from  vegetables. 
Emily.  From  what  does  soda  derive  its  name  ? 
Mrs.  B.  From  a  plant  called  by  us  soda,  and  by  the  Arabs 
Icali,  which  affords  it  in  great  abundance.     Kali  has,  indeed,  gi- 
ven its  name  to  the  alkalies  in  general. 

Caroline.  Does  soda  form  glass  and  soap  in' the  same  man- 
ner as  potash  ? 

*  A  very  pretty  experiment  on  the  change  of  colours  may  be  made 
as  follow?  :  Make  a  tincture,  by  pouring  Lolling  water  on  red  cab- 
bage and  let  it  stand  a  while.  Put  it  into  a  vial.  The  colour  will  be 
purple.  Take  two  wine  glasses,  and  into  one  put  a  few  drops  of  sul- 
phuric acid,  and  into  the  other  the  same  quantity  of  a  strong  solution 
of  potash.  So  little  of  either  will  do,  that  the  glasses  may  he  inverted 
for  a  moment.  Then  pour  the  tincture  int-»  each,  and  the  one  contain- 
ing the  acid  will  appear  a  most  beautiful  red,  and  the  other  as  beauti- 
ful a  green.  C. 


AMMONIA.  181 

Mrs.  B.  Yes,  it  does ;  it  is  of  equal  importance  in  the  arts, 
and  is  even  preferred  to  potash  for  some  purposes;  but  you 
will  not  be  able  to  distinguish  their  properties  till  we  examine 
the  compound  salts  which  they  form  with  acids ;  we  must 
therefore  leave  soda  for  the  present,  and  proceed  to  AMMONIA 

Or  the  VOLATILE  ALKALI. 

Emily.  I  long  to  hear  something  of  this  alkali ;  is  it  not  of 
the  same  nature  as  hartshorn  ? 

Mrs.  ft.  Yes  it  is,  as  you  will  see  by-and-bye.  This  alkali 
is  seldom  found  in  nature  in  its  pure  state ;  it  is  most  commonly 
extracted  from  a  com  pound  salt,  cal  led  sal  ammoniac,  which  was 
formerly  imported  from  Ammonia,  a  region  of  Libya,  from 
which  both  these  salts  and  the  alkali  derive  their  names.  The 
crystals  contained  in  this  bottle  are  specimens  of  this  salt, 
which  consist  of  a  combination  of  ammonia  and  muriatic  acid. 

Caroline.  Then  it  should  be  called  muriatic  of  ammonia ; 
for  though  I  am  ignorant  what  muriatic  acid  is,  yet  I  know  that 
its  combination  with  ammonia  cannot  but  be  so  called ;  and  J 
am  surprised  to  see  sal  ammoniac  inscribed  on  the  label. 

Mrs.  B  That  is  the  name  by  which  it  has  been  so  long 
known,  that  the  modern  chemists  have  not  yet  succeeded  in 
banishing  it  altogether  ;  and  it  is  still  sold  under  that  name  by 
druggists,  though  by  scientific  chemists  it  is  more  properly  call- 
ed muriat  of  ammonia. 

Caroline.  Both  the  popular  and  the  common  name  should 
be  inscribed  on  labels — this  would  soon  introduce  the  new  no- 
menclature. 

Emily.  By  what  means  can  the  ammonia  be  separated  from 
the  muriatic  acid  ? 

Mrs.  B.  By  chemical  attraction  ;  .but  this,  operation  is  too 
complicated  for  you  to  understand,  till  you  are  better  acquaint- 
ed with  the  agency  of  affinities. 

Emily.  And  when  extracted  from  the  salt,  what  kind  of  sub- 
stance is  ammonia  ? 

Mrs.  B.  Its  natural  form,  at  the  temperature  of  the  atmos- 
phere, when  free  from  combination,  is  that  of  gas  ;  and  in  this 
state  it  is  called  animoniacal gas.  But  it  mixes  very  readily 
with  water,  and  can  be  thus  obtained  in  a  liquid  form. 

Caroline.  You  said  that  ammonia  was  more  complicated  in 
its  composition  than  the  other  alkalies  ;  pray  of  what  principles 
does  it  consist  ? 

Mrs.  tf.  It  was  discovered  a  few  years  since,  by  Berthollet,  a, 
celebrated  French  chemist,  that  it  consisted  of  about  one  part 
of  hvdrogen  to  four  parjs  of  nitrogen.  Having  heated  ammo- 
niacal  gas  under  a  receiver,  by  causing  the  electrical  spark  to 

17 


1 82  AMMONIA. 

pass  repeatedly  through  it,  he  found  that  it  increased  consider- 
ably in  bulk,  los>t  all  its  alkaline  properties,  and  was  actually 
converted  into  hydrogen'and  nitrogen  gases  ;  and  from  the  latest 
and  most  accurate  experiments,  the  proportions  appear  to  be, 
one  volume^ef  nitrogen  gas  to  three  of  oxygen  gas.* 

Caroline.  Ammonia,  therefore,  has  not,,  like  the  two  other 
alkalies,  a  metallic  basis  ? 

j\>rs.  ti.  It  is  believed  that  it  has,  though  it  is  extremely  dif- 
ficult to  reconcile  that  idea  with  what  1  have  just  stated  of  its 
chemical  nature.  But  the  fact  is,  that  although  this  supposed 
metallic  basis  of  ammonia  has  never  been  obtained  distinct  and 
separate,  yet  both  Professor  Berzelius,  of  Stockholm,  and  Sir 
H.  Davy,  have  succeeded  in  forming  a  Combination  of  mercu- 
ry with  the  basis  of  ammonia,  which  has  so  much  the  appear- 
ance of  an  amalgam,  that  it  strongly  corroborates  the  idea  of 
ammonia  having  a  metallic  basis.t  But  these  theoretical  points 
are  full  of  difficulties  and  doubts,  and  it  would  be  useless  to 
dwell  any  longer  upon  them. 

Let  us  therefore  return  to  the  properties  of  volatile  alkali. 
Ammoniacal  pas  is  considerably  lighter  than  oxygen  gas,  and 
only  about  half  the  weight  of  atmospherical  air.  It  possesses 
most  of  the  properties  of  the  fixed  alkalies  ;  but  cannot  be  of  so 
much  use  in  the  arts  on  account  of  i<&  volatile  nature.  It  is, 
therefore,  never  employed  in  the  manufacture  of  glass,  but  it 
forms  soap  with  oils  equally  as  well  as  potash  and  soda  ;  it  re- 
sembles them  likewise  in  its  strong  attraction  for  water  ;  foi 
which  reason  it  can  be  collected  in  a  receiver  over  mercury 
only. 

Caroline.  I  do  not  understand  this  ? 

Mrs.  ;..  iJo  you  recollect  the  method  which  we  used  to  col- 
lect gases  in  a  glass  receiver  over  water  ? 

Caroline.  Perfectly. 

A.rs.  t'.  Ammouiacal  gas  has  so  strong  a  tendency  to  unite 
with  water,  that,  instead  of  passing  through  that  fluid,  it  would  be 
instantaneously  absorbed  by  it.  We  can  therefore  neither  use 
\vuter  for  that  purpose,  nor  any  other  liquid  of  which  water  is 
a  component  part;  so  that,  in  order  to  collect  this  gas,  we  are 

-    *  It  ought  to  be  hydrogen  gas.    C. 

"  t  'I  his  amalgam  is  easily  obtained,  by  placing  a  globule  of  mercury 
upon  a  piece  of  muriat,  or  carbonat  of  ammonia,  and  electrifying  this 
globule  by  the  Voltaic  battery.  The  globule  instantly  begins  to  ex- 
pand to  three  or  tour  times'  it3  former  size,  and  becomes  much  less 
fluid,  though  without  losing  its  metallic  lustre,  a  change  which  is  as- 
cribed to  the  metallic  basis  of  'ammonia  uniting  with  the  mercury,. 
This  is  an  extremely  curious  experini< 


AMMONIA.  183 

obliged  to  have  recourse  to  mercury,  (a  liquid  which  has  no  ac- 
tion upon  it,)  and  a  mercurial  bath  is  used  instead  of  a  water 
bath,  such  as  we  employed  on  former  occasions.  Water  im- 
pregnated with  this  gas  is  nothing  more  than  the  fluid  which 
you  mentioned  at  the  beginning  of  the  conversation — hartshorn ; 
it  is  theammoniacal  gas  escaping  from  the  water  which  gives  it 
so  powerful  a  smell.* 

Emily.  But  there  is  no  appearance  of  effervescence  in  harts- 
horn. 

Mrs.  B.  Because  the  particles  of  gas  that  rise  from  the  wa- 
ier  are  too  subtle  and  minute  for  their  effect  to  be  visible. 

Water  diminishes  in  density,  by  being  impregnated  with 
ammoniacal  gas  ;  and  this  augmentation  of  bulk  increases  its 
capacity  for  caloric. 

Emily.  In  making  hartshorn,  then,  or  impregnating  water 
with  ammonia,  heat  must  be  absorbed,  and  cold  produced  ? 

Mrs.  B.  That  effect  would  take  place  if  it  was  not  counter- 
acted by  another  circumstance  ;  the  gas  is  liquefied  by  incorpo- 
rating with  the  water,  and  gives  out  its  latent  heat.  The  con- 
densation of  the  gas  more  than  counterbalances  the  expansion 
of  the  water ;  therefore,  upon  the  whole,  heat  is  produced. — But 
if  you  dissolve  ammoniacal  gas  with  ice  or  snow,  cold  is  produ- 
ced.— Can  you  account  for  that  ? 

Emily.  The  gas,  in  being  condensed  into  a  liquid,  must  give 
out  heat;  and,  on  the  other  hand,  the  snow  or  ice,  in  being 
rarefied  into  a  liquid,  must  absorb  heat ;  so  that,  between  the 
opposite  effects,  I  should  have  supposed  the  original  tempera- 
ture would  have  been  preserved. 

Mrs.  B.  But  you  have  forgotten  to  take  into  the  account  the 

*  To  obtain  ammoniacal  gas,  mix  together  equal  parts  of  muriate 
of  ammonia,  and  dry  burnt  lime;  af'er  pulverizing  each  separately, 
•:ub  them  together  in  a  mortar  ;  put  them  into  a  retort  and  apply  the 
ijfeat  of  a  ia.mp.  Or,  the  common  spirit  of  sal.  ammoniac  may  be  heat- 
ed in  a  retort  in  the  same  way.  To  collect  and  retain.the  gas  without 
:t  mercurial  bath,  fix  a  receiver  or  bottle  in  an  inverted  position,  and 
•  •-onnect  to  the  retort  a  tube,  which  introduce  up  into  the  receiver  so 
'hat  it  nearly  reaches  the  bottom.  A*  the  gas  comes  over,  its  levity 
is  such,  that  it  fills  the  upper  part  of  the  receiver  first,  gradually  dat- 
ing out  the  air.  and  taking  its  place.  To  keep  it  for  any  considerable 
lime,  the  receiver  must  be  stopped.  A  pretty  experiment  may  be 
made  by  introducing  up  into  the  receiver  with  the  ammonia,  some  mu- 
riatie  gas.  Both  gases  are  invissible  until  they  arc;  brought  tog-ether, 
when  they  unite,  forming  a  dense  white  cloud,  and  fall  down  ia  the 
solid  form  of  muriate  of  ammonia.  The  muriatic  gas  is  obtained  by 
pouring  sulphuric  acid  on  common  salt,  and  applying  the  heat  of  a 
lamp.  It  may  be  sent  up  into  the  receiver  in  the  way  above  described 
or  ammonia.  C. 


184  AMMONIA. 

rarefaction  of  the  water  (or  melted  ice)  by  the  impregnation  o? 
the  gas ;  and  this  is  the  cause  of  the  cold  which  is  ultimately 
produced. 

Caroline.  Is  the  sal  volatile  (the  smell  of  which  so  strongly 
resembles  hartshorn)  likewise  a  preparation  of  ammonia  ? 

Mrs.  B.  It  is  carbonat  of  ammonia  dissolved  in  water;  and 
which,  in  its  concrete  state,  is  commonly  called  salts  of  harts- 
horn.  Ammonia  is  caustic,  like  the  fixed  alkalies,  as  you  may 
judge  by  the  pungent  eflects  of  hartshorn,  which  cannot  be  ta- 
.ken  internally,  nor  applied  to  delicate  external  parts,  without 
being  plentifully  diluted  with  water. — Oil  and  acids  are  very 
excellent  antidotes  for  alkaline  poisons  ;  can  you  guess  why  ? 

Caroline.  Perhaps,  because  the  oil  combines  with  the  alkalf, 
and  forms  soap,  and  thus  destroys  its  caustic  properties  ;  and 
the  acid  converts  it  into  a  compound  salt,  which,  I  suppose,  is 
not  so  pernicious  as  caustic  alkali. 

Mrs.  B.  Precisely  so. 

Ammoniacal  gas,  if  it  be  mixed  with  atmospherical  air,  and 
a  burning  taper  repeatedly  plunged  into  it,  will  burn  with  a 
large  flame  of  a  pecular  yellow  colour. 

Emily.  But  pray  tell  me,  can  ammonia  be  procured  from 
this  Lybian  salt  only  ? 

Mrs.  B.  So  far  from  it,  that  it  is  contained  in,  and  may  be 
extracted  from,  all  animal  substances  whatever.  Hydrogen 
and  nitrogen  are  two  of  the  chief  constituents  of  animal  matter; 
it  is  therefore  not  surprising  that  they  should  occasionally  meet 
and  combine  in  those  proportions  that  compose  ammonia.  But 
this  alkali  is  more  frequently  generated  by  the  spontaneous  de- 
composition of  animal  substances  ;  the  hydrogen  and  nitrogen 
gases  that  arise  from  putrified  bodies  combine,  and  form  the 
volatile  alkali. 

Muriat  of  ammonia,  instead  of  being  exclusively  brought 
from  Lybia,  as  it  originally  was,  is  now  chiefly  prepared  in  Eu- 
rope, by  chemical  processes.  Ammonia,  although  principally 
extracted  from  this  salt,  can  also  be  produced  by  a  great  varie- 
ty of  other  substances.  The  horns  of  cattle,  especially  those  of 
deer,  yield  it  in  abundance,  and  it  is  from  this  circumstance  that 
a  solution  of  ammonia  in  water  has  been  called  hartshorn.  It 
may  likewise  be  procured  from  wool,  flesh  and  bones ;  in  a 
word,  any  animal  substance  whatever  yields  it  by  decomposi- 
tion. 

We  shall  now  lay  aside  the  alkalies,  however  important  the 
subject  may  be,  till  we  treat  of  their  combination  with  acidr- 
The  ne,xt  time  we  meet  we  shall  examine  the  earths, 


EARTHS.  185 


CONVERSATION  XV. 

ON  EARTHS. 

Mrs.  B.  THE  EARTHS,  which  we  are  to-day  to  examine,  are 
nine  in  number : 

SILEX,  STRONTITES,* 

ALUMINE,  YTTRIA, 

BARYTES,*  GLUCINA, 

LIME,*  Z1RCONIA. 
MAGNESTA;* 

The  last  three  are  of  late  discovery;  their  properties  are  but 
imperfectly  known ;  and,  as  they  have  not  yet  been  applied  to 
use,  it  will  be  unnecessary  to  enter  into  any  particulars  respecting 
them  ;  we  shall  confine  our  remarks,  therefore  to  the  first  five. 
They  are  composed,  as  you  have  already  learnt,  of  a  metallic 
basis  combined  with  oxygen  ;  and,  from  this  circumstance,  are 
incombustible. 

Caroline.  Yet  I  have  seen  turf  burnt  in  the  country,  and  it 
makes  an  excellent  fire;  the  earth  becomes  red  hot,  and  produ- 
ces a  very  great  quantity  of  heat. 

Mrs,  B.  It  is  not  the  earth  that  burns,  my  dear,  but  the  roots, 
grass,  and  other  remnants  of  vegetables  that  are  intermixed 
with  it.  The  caloric,  which  is  produced  by  the  combustion  of 
these  substances,  makes  the  earth  red  hot,  and  this  being  a  bad 
conductor  of  heat,  retains  its  caloric  a  long  time  ;  but  were  you 
to  examine  it  when  cooled,  you  would  find  that  it  had  not  ab- 
sorbed one  particle  of  oxygen,  nor  suffered  any  alteration  from 
the  fire.  Earth  is,  however,  from  the  circumstance  just  men- 
tioned, an  excellent  radiator  df  heat,  and  owes  its  utility,  when 
mixed  with  fuel,  solely  to  that  property.  It  is  in  this  point  of 
view  that  Count  Rum  ford  has  recommended  balls  of  incombus- 

*  There  is  less  evidence  that  these  four  earths  a  e  composed  of 
metallic  bases  than  there  is  in  the  case  of  ammonia,  which  it  will  be 
remembered  \\jas  supposed  in  have  formed  an  amalgam  \yith  mercury, 
and  on  this  account  was  supposed  to  have  had  a  metallic  basis.  Of 
the  other  earths,  no  one  except  Dr.  Clarke  of  Cambridge,  En«f.  has 
pretended  to  offer  any  but  conjectural  evidence  of  their  metallic  nature. 
This  gentleman,  on  subjecting  them  to  the  heat  of  the  blow-pipe,  charg° 
?d  with  oxygen  and  hydrogen,  was  led  to  believe  he  had  obtained 
their  metallic  bases.  But  as  his  experiments  have  been  repeated  at 
the  Royal  Institution  without  success,  it  is  now  understood  that  the  Dr, 
must  have  been  mistaken.  C. 


186 

tible  substances  to  be  arranged  in  fire-places,  and  mixed  witii 
the  coals,  by  which  means  the  caloric  disengaged  by  the  com- 
bustion of  the  latter  is  more  perfectly  reflected  into  the  room, 
and  an  expense  of  fuel  is  saved. 

Emily.  I  expected  that  the  list  of  earths  would  be  much 
more  considerable.  When  I  think  of  the  great  variety  of  soils, 
I  am  astonished  that  there  is  not  a  greater  number  of  earths  to 
form  them. 

Mrs.  B.  You  might  indeed,  almost  confine  that  number  to 
four;  for  barytes,  strontites,  and  the  others  of  late  discovery, 
act  but  so  small  a  part  in  this  great  theatre,  that  they  cannot  be 
reckoned  as  essential  to  the  general  formation  of  the  globe. 
And  you  must  not  confine  your  idea  of  earths  to  the  formation 
of  soil ;  for  rock,  marble,  chalk,  slate,  sand,  flint,  and  all  kinds 
of  stones,  from  the  precious  jewels  to  the  commonest  pebbles  ; 
In  a  word,  all  the  immense  variety  of  mineral  products  may  be 
referred  to  some  of  these  earths,  either  in  a  simple  state,  or  com- 
bined the  one  with  the  other,  or  blended  with  other  ingredients. 

Caroline.  Precious  stones  composed  of  earth  !  That  seems 
very  difficult  to  conceive. 

E-nily.  Is  it  more  extraordinary  than  that  the  most  precious 
of  ail  jewels,  diamond,  should  be  composed  of  carbon  ?  But  di- 
amond forms  an  exception,  Mrs.  B. ;  for,  though  a  stone,  it  is 
not  composed  of  earth. 

Mrs.  B.  I  did  not  specify  the  exception,  as  I  knew  you  were 
so  wel'  a  quainted  with  it.  Besides,  I  would  call  a  diamond  a 
tnineirl  rather  than  a  stone,  as  the  latter  term  always  implies 
the  presence  of  some  earth. 

Caroline.  I  cannot  conceive  how  such  coarse  materials  can 
be  converted  into  such  beautiful  productions. 

Mrs.  B.  We  are  very  far  from  understanding  all  the  secret 
resources  of  nature ;  but  I  do  not  think  the  spontaneous  forma- 
tion of  the  crystals,  which  we  call  precious  stones,  one  of  the 
Most  difficult  phenomena  to  comprehend. 

By  the  slow  and  regular  work  of  ages,  perhaps  of  hundreds  of 
ages,  these  earths  may  be  gradually  dissolved  by  water,  and  as 
gradually  deposited  by  their  solvent  in  the  undisturbed  process 
of  crystallisation.  The  regular  arrangement  of  their  particles, 
during  their  re-union  in  a  solid  mass,  gives  them  that  brilliancy, 
transparency,  and  beauty,  for  which  they  are  so  much  admired  ; 
and  renders  them  in  appearance  so  totally  different  from  their 
lude  and  primitive  ingredients. 

Caroline.  But  how  does  it  happen  that  they  are  spontane- 
ously dissolved,  and  afterwards  crystallised  r 

./km*.  B.  The  scarcity  of  many  kinds  of  crystals,  as  rubies. 


EARTHS.  187 

emeralds,  topazes,  &c.  shows  that  their  formation  is  not  an  ope- 
ration very  easily  carried  on  in  nature.  But  cannot  you  ima- 
gine that  when  water,  holding  in  solution  some  particles  of  earth, 
filters  through  the  crevices  of  hills  or  mountains,  and  at  length 
dribbles  into  some  cavern,  each  successive  drop  may  be  slowly 
evaporated,  leaving  behind  it  the  particle  of  earth  which  it  held 
in  solution?  You  know  that  crystallisation  is  more  regular  and 
perfect,  in  proportion  as  the  evaporation  of  the  solvent  is  slow 
and  uniform;  nature,  therefore,  who  knows  no  limit  of  time, 
has,  in  all  works  of  this  kind,  an  infinite  advantage  over  any 
artist  who  attempts  to  imitate  such  productions. 

Emily.  I  can  now  conceive  that  the  arrangement  of  the  par- 
ticles of  earth,  during  crystallisation,  may  be  such  as  to  occa- 
sion transparency,  by  admitting  a  free  passage  to  the  rays  of 
light ;  but  I  cannot  understand  why  crystallised  earths  should 
assume  such  beautiful  colours  as  most  of  them  do.  Sapphire, 
for  instance,  is  of  a  celestial  blue ;  ruby,  a  deep  red  ;  topaz,  a 
brilliant  yellow  ? 

Mrs.  B.  Nothing  is  more  simple  than  to  suppose  that  the  ar- 
rangement of  their  particles  is  such,  as  to  transmit  some  of  the 
coloured  rays  of  light,  and  to  reflect  others,  in  which  case  the 
stone  must  appear  of  the  colour  of  the  rays  which  it  reflects. 
But  besides,  it  frequently  happens  that  the  colour  of  a  stone  is 
owing  to  a  mixture  of  some  metallic  matter. 

Caroline.  Pray,  are  the  different  kinds  of  precious  stones 
each  composed  of  one  individual  earth,  or  are  they  formed  of  a 
combination  of  several  earths  ? 

Mrs.  B.  A  great  variety  of  materials  enters  into  the  compo- 
sition of  most  of  them ;  not  only  several  earths,  but  sometimes 
salts  and  metals.  The  earths,  however,  in  their  simple  state, 
frequently  form  very  beautiful  crystals;  and,  indeed,  it  is  in 
that  state  only  that  they  can  be  obtained  perfectly  pure. 

Emily.  Is  not  the  Derbyshire  spar  produced  by  the  crystalli- 
sation of  earths,  in  the  way  you  have  just  explained  ?  I  have 
been  in  some  of  the  subterraneous  caverns  where  it  is  found, 
which  are  similar  to  those  you  have  described. 

Mrs.  B.  Yes;  but  this  spar  is  a  very  imperfect  specimen  of 
crystallisation  ;*  it  consists  of  a  variety  of  ingredients  confused- 
ly bleded  together,  as  you  may  judge  by  its  opacity,  and  by  the 
various  colours  and  appearances  which  it  exhibits. 

But,  in  examining  the  earths  in  their  most  perfect  and  agree- 

*  The  Derbyshire  spar  is  composed  of  lime  and  fluoric  acid:  hence 
it  is  called  Jluate  of  li/ne.  The  colours  are  owing  to  intermixture  with 
metallic  oxides.  It  is  a  very  beautiful  rain-  ral,  and  instead  of  being 
opake  it  is  generally  translucent,  or  nearly  transparent.  C. 


188  SILEX. 

able  form,  we  must  not  lose  sight  of  that  state  in  which  they 
are  commonly  found,  and  which,  if  less  pleasing  to  the  eye,  is 
far  more  interesting  by  its  utility. 

All  the  earths  are  more  or  less  endowed  with  alkaline  prop- 
erties ;  but  th*ere  are  four,  barytes,  magnesia,  lime,  and  stron- 
tites,  which  are  called  alkaline  earths,  because  they  possess 
those  qualities  in  so  great  a  degree,  as  to  entitle  them,  in  most 
respects,  to  the  rank  of  alkalies.  They  combine  and  form 
compound  salts  with  acids,  in  the  same  way  as  alkalies  ;  they 
are,  like  them,  susceptible  of  a  considerable  degree  of  causticity, 
and  are  acted  upon  in  a  similar  manner  by  chemical  tests. — The 
remaining  earths,  silex  and  aiumine,  with  one  or  two  others  of 
late  discovery,  are  in  some  degree  more  earthy,  that  is  to  say, 
they  possess  more  completely  the  properties  common  to  all  the 
earths,  which  are,  insipidity,  dryness,  unalterableness  in  the 
fire,  in  fusibility,  &c. 

Caroline.  Yet,  did  you  not  tell  us  that  silex,  or  siliceous 
earth,  when  mixed  with  an  alkali,  was  fusible,  and  run  into 
glass  ? 

Mrs.  B.  Yes,  my  dear ;  but  the  characteristic  properties  of 
earths,  which  I  have  mentioned,  are  to  be  considered  as  belong- 
ing to  them  in  a  state  of  purity  only ;  a  state  in  which  they  are 
very  seldom  to  be  met  with  in  nature. — Besides  these  general 
properties,  each  earth  has  its  own  specific  characters,  by  which 
it  is  distinguished  from  any  other  substance. — Let  us  therefore 
review  them  separately. 

SILEX.  or  SILICA,  abounds  in  flint,  sand,  sand-stone,  agate, 
jasper,  &e. ;  it  forms  the  basis  of  many  precious  stones,  and 
particularly  of  those  which  strike  fire  with  steel.  It  is  rough 
to  the  touch,  scratches  and  wears  away  metals ;  it  is  acted  up- 
on by  no  acid  but  the  fluoric,  and  is  not  soluble  in  water  by 
any  known  process  ;  but  nature  certainly  dissolves  it  by  means 
with  which  we  are  unacquainted,  and  thus  produces  a  variety 
ef  siliceous  crystals,  and  amongst  these  rock  crystal^  which  is 
the  purest  specimen  of  this  earth.  Silex  appears  to  hfcve  been 
intended  by  Providence  to  form  the  solid  basis  of  the  globe,  to 
serve  as  a  foundation  for  the  original  mountains,  and  give  them 
that  hardness  and  durability  which  has  enabled  them  to  resist 
the  various  revolutions  which  the  surface  of  the  earth  has  suc- 
cessively undergone.  From  these  mountains  siliceous  rocks 
have,  during  the  course  of  ages,  been  gradually  detached  by 
torrents  of  water,  and  brought  down  in  fragments ;  these,  in 
the  violence  and  rapidity  of  their  descent,  are  sometimes  crum- 
bled to  sand,  and  in  this  state  form  the  beds  of  rivers  and  of 
the  sea,  chiefly  composed  of  siliceous  materials.  Sometii»€s 


SILEX.  189 

the  fragments  are  broken  without  being  pulverised  by  their 
fall,  and  assume  the  form  of  pebbles,  which  gradually  become 
rounded  and  polished. 

Emily.  Pray  what  is  the  true  colour  of  silex,  which  forms 
such  a  variety  of  different  coloured  substances  ?  Sand  is  brown, 
flint  is  nearly  black,  and  precious  stones  are  of  all  colours. 

Mrs.  B.  Pure  silex,  such  as  is  found  only  in  the  chemist's  la- 
boratory, is  perfectly  white,  and  the  various  colours  which  it 
assumes,  in  the  different  substances  you  have  just  mentioned, 
proceed  from  the  different  ingredients  with  which  it  is  mixed  in 
them. 

Caroline.  I  wonder  that  silex  is  not  more  valuable,  since  it 
forms  the  basis  of  so  many  precious  stones.* 

Mrs.  B.  You  must  not  forget  that  the  value  we  set  upon  pre- 
cious stones  depends  in  a  great  measure  upon  the  scarcity  with 
which  nature  affords  them;  for,  were  those  productions  either 
common  or  perfectly  imitable  by  art,  they  would  no  longer, 
notwithstanding  their  beauty,  be  so  highly  esteemed.  But  the 
real  value  of  siliceous  earth,  in  many  of  the  most  useful  arts,  is 
very  extensive.  Mixed  with  clay,  it  forms  the  basis  of  all  the 
various  kinds  of  earthern  ware,  from  the  most  common  uten- 
sils to  the  most  refined  ornaments. 

Emily.  And  we  must  recollect  its  importance  to  the  forma- 
tion of  glass  with  potash. 

Mrs.  B.  Nor  should  we  omit  to  mention,  likewise,  many 
other  important  uses  of  silex,  such  as  being  the  chief  ingredi- 
ent of  some  of  the  most  durable  cements,  of  mortar,  &c. 

I  said  before  that  siliceous  earth  combined  with  no  acid  but 
the  fluoric ;  it  is  for  this  reason  that  glass  is  liable  to  be  attack- 
ed by  that  acid  only,  which,  from  its  strong  affinity  for  silex, 
forces  that  substance  from  its  combination  with  the  potash,  and 
thus  destroys  the  glass. 

We  will  now  hasten  to  proceed  to  the  other  earths,  for  I  am 
rather  apprehensive  of  your  growing  weary  of  this  part  of  our 
subject. 

Caroline.  I  confess  that  the  history  of  the  earths  is  not  quite 
so  entertaining  as  that  of  the  simple  substances. 

Mrs.  B.  Perhaps  not ;  but  it  is  absolutely  indispensable  that 
you  should  know  something  of  them ;  for  they  form  the  basis 
of  so  many  interesting  and  important  compounds,  that  their 
total  omission  would  throw  great  obscurity  on  our  general  out-. 

*  The  bases  of  some  of  the  most  costly  gems,  as  sapphire,  ruby  ami 
j  are  alumine.     C, 


190  ALUMINE. 

line  of  chemical  science.     We  shall,  however,  review  them  in 
as  cursory  a  manner  as  the  subject  can  admit  of. 

ALUMINE  derives  its  name  from  a  compound  salt  called  alum9 
of  which  it  forms  the  basis. 

Caroline.  But  it  ought  to  be  just  the  contrary,  Mrs.  B.  ;  the 
simple  body  should  give,  instead  of  taking,  its  name  from  the 
compound. 

Mrs.  B.  That  is  true  ;  but  as  the  compound  salt  was  known 
long  before  its  basis  was  discovered,  it  was  very  natural  that 
when  the  earth  was  at  length  separated  from  the  acid,  it  should 
derive  its  name  from  the  compound  from  which  it  was  obtain- 
ed. However,  to  remove  your  scruples,  we  will  call  the  salt 
according  to  the  new  nomenclature,  sulphat  of  aiumine.  From 
this  combination,  alumioe  may  be  obtained  in  its  pure  state  ;  it 
is  then  soft  to  the  touch,  makes :a  paste  with  water,  and  hardens 
in  the  fire.  In  nature,  it  is  found  chiefly  in  clay,  which  con- 
tains a  considerable  proportion  of  this  earth ;  it  is  very  abun- 
dant in  fuller's  earth,  slate,  and  a  variety  of  other  mineral  pro- 
ductions. There  is  indeed  scarcely  any  mineral  substance  more 
useful  to  mankind  than  aiumine.  In  the  state  of  clay,  it  forms 
large  strata  of  the  earth,  gives  consistency  to  the  soil  of  valleys, 
and  of  all  low  and  damp  spots,  such  as  swamps  and  marshes. 
The  beds  of  lakes,  ponds,t  and  springs,  are  almost  entirely 
of  clay  ;  instead  of  allowing  of  the  filtration  of  water,  as  sand 
does,  it  forms  an  impenetrable  bottom,  and  by  this  means 
water  is  accumulated  in  the  caverns  of  the  earth,  producing 
those  reservoirs  whence  springs  issue,  and  spout  out  at  the  sur- 
face. 

Emily.  I  always  thought  that  these  subterraneous  reservoirs 
of  water  were  bedded  by  some  hard  stone,  or  rock,  which  the 
water  could  not  penetrate. 

Mrs.  B.  That  is  not  the  case  ;  for  in  the  course  of  time  wa- 
ter would  penetrate,  or  wear  away  silex,  or  any  other  kind  of 
stone,  while  it  is  effectually  stopped  by  clay,  or  aiumine. 

The  solid  compact  soils,  such  as  are  fit  for  corn,  owe  their 
consistence  in  a  great  measure  to  aiumine  ;  this  earth  is  there- 
fore used  to  improve  sandy  or  chalky  soils,  which  do  not  retain 
a  sufficient  quantity  of  water  for  the  purpose  of  vegetation. 

Aiumine  is  the  most  essential  ingredient  in  all  potteries.  It 
enters  into  the  composition  of  brick,  as  well  as  that  of  the  finest 
porcelain  :  the  addition  of  silex  and  water  hardens  it,  renders 
it  susceptible  of  a  degree  of  vitrification,  and  makes  it  perfectly 
fit  for  its  various  purposes. 

Caroline.  I  can  scarcely  conceive  that  brick  and  china  should 
be  made  of  the  same  materials* 


BARYTfiS.  191 

Mrs.  B.  Brick  consists  almost  entirely  of  baked  clay ;  but 
a  certain  proportion  of  silex  is  esset.t  al  to  the  formation  of 
earthen  or  stone  ware.  In  common  potteries  sand  is  used  for 
that  purpose ;  a  more  pure  silex  is,*  I  believe,  necessary  for 
the  composition  of  porcelain,  as  well  as  a  finer  kind  of  clay  ; 
and  these  materials  are,  no  doubt,  more  carefully  prepared, 
and  curiously  wrought,  in  the  one  case  than  in  the  other.  Por- 
celain owes  its  beautiful  semi-transparency  to  a  commencement 
of  vitrification. 

Emily.  But  the  commonest  earthen-ware,  though  not  trans- 
parent, is  covered  with  a  kind  of  glazing. 

Mrs.  B.  That  precaution  is  equally  necessary  for  use  as  for 
beauty,  as  the  ware  would  be  liable  to  be  spoiled  and  corroded 
by  a  variety  of  substances,  if  not  covered  with  a  coating  of  this 
kind.  In  porcelain  it  consists  of  enamel,  which  is  a  fine  white 
opaque  glass,  formed  of  metallic  oxyds,  sand,  salts,  and  such 
other  materials  as  are  susceptible  of  vitrification.  The  gla- 
zing of  common  earthen-ware  is  made  chiefly  of  oxyd  of  lead, 
or  sometimes  merely  of  salt,  which,  when  thinly  spread  over 
earthen  vessels,  will,  at  a  certain  heat,  run  into  opaque  glass. 

Car<line.  And  of  what  nature  are  the  colours  which  are  us- 
ed for  painting  porcelain  ? 

Mr*.  B.  They  are  all  composed  of  metallic  oxyds,  so  that 
these  colours,,  instead  of  receiving:  injury  from  the  application 
of  fire,  are  strengthened  and  developed  by  its  action,  which 
causes  them  to  undergo  different  degrees  of  oxydation. 

Alumine  and  silex  are  not  only  often  combined  by  art,  but 
they  have  in  nature  a  very  strong  tendency  to  unite,  and  are 
found  combined,  in  different  proportions,  in  various  gems  and 
other  minerals.  Indeed,  many  of  the  precious  stones,  such  as 
ruby,  oriental  sapphire,  amethyst,  <  &c.  consist  chiefly  of  al- 
umine. 

We  may  now  proceed  to  the  alkaline  earths.  I  shall  say 
but  a  few  words  on  BARYTES,  as  it  is  hardly  ever  used,  except 
in  chemical  laboratories.  It  is  remarkable  for  its  great  weight, 
and  its  strong  alkaline  properties,  such  as  destroying  animal 
substances,  turning  green  some  blue  vegetable  colours,  ;md 
showing  a  powerful  attraction  for  acids  $  this  last  property  it 
possesses  to  such  a  degree,  particularly  with  regard  to  the  sul- 
phuric acid,  that  it  will  always  detect  its  presence  in  any  sub- 

*  Porcelain  clay,  of  which  china  ware  is  made,  is  found  among  gra- 
nite rocks,  and  seems  to  owe  its  oriei'i  to  the  decomposition  of  a  min- 
eral calle  d  feldspar.  Its  composition  i?  silex  and  alumine,  silex  being 
the  predominant  ingredient.  C. 

t  The  amethyst  is  almost  entirely  composed  of  imex.    C. 


192  LIME. 

stance  or  combination  whatever,  by  immediately  uniting  with 
it,  and  forming  a  sulphat  of  barytes.  This  renders  it  a  very 
valuable  chemical  test.  It  is  found  pretty  abundantly  in  na- 
ture in  the  state  of  carbonat,*  from  which  the  pure  earth  can 
be  easily  separated. 

The  next  earth  we  have  to  consider  is  LIME.  This  is  a  sub- 
stance of  too  great  and  general  importance  to  be  passed  over 
so  slightly  as  the  last. 

Lime  is  strongly  alkaline.  In  nature  it  is  not  met  with  in  its 
simple  state,  as  its  affinity  for  water  and  carbonic  acid  is  so 
great,  that  it  is  always  found  combined  with  these  substances, 
with  which  it  forms  the  common  lime-stone;  but  it  is  separated 
in  the  kiln  from  these  ingredients,  which  are  volatilised  when- 
ever a  sufficient  degree  of  heat  is  applied. 

Emily.  Pure  lime,  then,  is  nothing  but  lime-stone,  which  has 
been  deprived,  in  the  kiln,  of  its  water  and  carbonic  acid  ? 

j\irs.  ft.  Precisely  :  in  this  state  it  is  called  quick-lime,  and 
it  is  so  caustic,  that  it  is  capable  of  decomposing  the  dead  bo- 
dies of  animals  very  rapidly,  without  their  undergoing  the  pro- 
cess of  putrefaction. — 1  have  here  some  quick-lime,  which  is 
kept  carefully  corked  up  in  a  bottle,  to  prevent  the  access  of 
air  ;  for  were  it  all  exposed  to  the  atmosphere,  it  would  absorb 
both  moisture  and  carbonic  acid  gas  from  it,  and  be  soon  slaked. 
Here  is  also  some  lime-stone — we  shall  pour  a  little  water  on 
each,  and  observe  the  effects  that  result  from  it. 

Caroline.  How  the  quick-lime  hisses  !  It  is  become  exces- 
sively hot  ! — It  swells,  and  now  it  bursts  and  crumbles  to  pow- 
der, while  the  water  appears  to  produce  no  kind  of  alteration 
on  the  lime-stone. 

Mrs.  />".  Because  the  lime-stone  is  already  saturated  with 
water,  whilst  the  quick-lime,  which  has  been  deprived  of  it 
in  the  kiln,  combines  with  it  with  very  great  avidity,  and 
produces  this  prodigious  disengagement  of  heat,  the  cause  of 
which  I  formerly  explained  to  you  ;  do  you  recollect  it  ? 

Emily.  Yes  5  you  said  that  the  heat  did  not  proceed  from 
the  lime,  but  from  the  water  which  was  solidified,  and  thus 
parted  with  its  heat  of  liquidity. 

Mrs.  B.  Very  well.  If  we  continue  to  add  successive  quan- 
ties  of  water  to  the  lime  after  being  slaked  and  crumbled  as  you 
see,  it  will  then  gradually  be  diffused  in  the  water,  till  it  will  at 
length  be  dissolved  in  it,  and  entirely  disappear ;  but  for  this 

*  The  native  carbonate  of  barytes  is  a  rare  mineral.  It  is  a  virulent 
poison.  The  sulphate  of  barytes  is  found  in  considerable  abundance 


LIMfc.  i<}3 

purpose  it  requires  no  less  than  700  times  its  weight  of  water. 
This  solution  is  called  lime  water.* 

Caroline.  How  very  small,  then,  is  the  proportion  of  lime 
dissolved  ! 

J\-frs.  IB.  Barytes  is  still  of  more  difficult  solution  5  it  dis- 
solves only  in  900  times  its  weight  of  water ;  but  it  is  much 
more  soluble  in  the  state  of  crystals.  The  liquid  contained  in 
this  bottle  is  lime-water  ;  it  is  often  used  as  a  medicine,  chiefly, 
I  believe,  for  the  purpose  of  combining  with,  and  neutralising, 
the  superabundant  acid  which  it  meets  with  in  the  stomach. 

bmity.  I  am  surprised  that  it  is  so  perfectly  clear;  it  does 
not  at  all  partake  of  the  whiteness  of  the  lime. 

Mrs.  B.  Have  you  forgotten  that,  in  solutions,  the  solid  bo- 
dy is  so  minutely  subdivided  by  the  fluid  as  to  become  invisi- 
ble, and  therefore  will  not  in  the  least  degree  impair  the  trans- 
parency of  the  solvent? 

I  said  that  the  attraction  of  lime  for  carbonic  acid  was  so 
strong,  that  it  would  absorb  it  from  the  atmosphere.  We  may 
see  this  etfect  by  exposing  a  glass  of  lime-water  to  the  air ;  the 
lime  will  then  separate  from  the  water,  combine  with  the  car- 
bonic acid,  and  re-appear  on  the  surface  in  the  form  of  a  white 
fii.ii,  which  is  carbonatof  lime,  commonly  called  chalk. 

Caroline.  Chalk  is,  then,  a  compound  salt!  I  never  should 
have  supposed  that  those  immense  beds  of  chalk,  that  we  see 
in  many  parts  of  the  country,  were  a  salt. — Now,  the  white  film 
begins  to  appear  on  the  surface  of  the  <  ateV ;  but  it  is  far  from 
resembling  hard  solid  chalk. 

Mrs.  B.  That  is  owing  to  its  state  of  extreme  division  ;  in  a 
little  time  it  will  collect  into  a  more  compact  mass,  and  subside 
at  the  bottom  of  the  glass. 

If  you  breathe  into  lime-water,  the  carbonic  acid,  which  is 
mixed  with  the  air  that  you  expire,  \vi!l  produce  the  same  ef- 
fect. It  is  an  experiment  very  easily  made ; — I  shall  poui 
some  lime-water  into  this  glass  tube,  and,  by  breathing  repeat- 
edly into  it,  you  will  soon  perceive  a  precipitation  of  chalk — 

Emily.  I  see  already  a  small  white  cloud  formed. 

Mrs.  B.  It  is  composed  of  minute  particles  of  chalk  ;  at  pres- 
ent it  floats  in  the  water,  but  it  will  soon  subside. 

Carbonat  of  lime,  or  c^ialk,  you  see,  is  insoluble  in  water,, 
since  the  lime  which  was  dissolved  re-appears  when  converted 

*  To  make  lime  water,  take  a  piece  of'  well  burned  lime  about  the 
size  of  a  heiPs  egg,  put  it  into  au  earthen  dish,  and  sprinkle  water  oa 
it.  till  it  falls  into  powder  :  Then  pour  on  two  quarts  of  boiling1  water, 
and  s»ir  it  several  times,  alter  the  lime  ha?  settled,  ;  pour  off  the  clear 
water  and  cork  it  up  tor  use.  C. 

18 


194  LIME. 

into  chalk ;  but  you  must  take  notice  of  a  very  singular  circum- 
stance, which  is,  that  chalk  is  soluble  in  water  impregnated  with 
carbonic  acid. 

Caroline.  It  is  very  curious,  indeed,  that  carbonic  acid  gas 
should  render  lime  soluble  in  one  instance,  and  insoluble  in  the 
other  ! 

Mrs.  B.  I  have  here  a  bottle  of  Seltzer  water,  which,  you 
know,  is  strongly  impregnated  with  carbonic  acid  : — let  us 
pour  a  little  of  it  into  a  glass  of  lime-water.  You  see  that  it  im- 
mediately forms  a  precipitation  of  carbonat  of  lime  ? 

Emily.   Yes,  a  white  cloud  appears. 

Mrs.  B.  I  shall  now  pour  an  additional  quantity  of  the  Selt- 
zer water  into  the  lime-water — 

Emily.  How  singular !  The  cloud  is  re-dissolved,  and  the 
liquid  is  again  transparent. 

Mrs.  B.  All  the  mystery  depends  upon  this  circumstance, 
that  carbonat  of  lime  is  soluble  in  carbonic  acid,  whilst  it  is  in- 
soluble in  water  ;  the  first  quantity  of  carbonic  acid,  therefore, 
which  I  introduced  into  the  lime-water,  was  employed  in  form- 
ing the  carbonat  of  lime,  which  remained  visible,  until  an  addi- 
tional quantity  of  carbonic  acid  dissolved  it.  Thus,  you  see, 
when  the  lime  and  carbonic  acid  are  in  proper  proportions  to 
form  chalk,  the  white  cloud  appears,  but  when  the  acid  predom- 
inates, the  chalk  is  no  sooner  formed  than  it  is  dissolved. 

Caroline.  That  is  now  the  case;  but  let  us  try  whether  a 
further  addition  of  lime-water  will  again  precipitate  the  chalk. 

Emily.  It  does,  indeed!  The  cloud  re  appears,  because,  I 
suppose,  there  is  now  no  more  of  the  carbonic  acid  than  is  ne- 
cessary to  form  chalk;  and,  in  order  to  dissolve  the  chalk,  a 
superabundance  of  acid  is  required. 

Mrs.  B.  We  have,  I  think,  carried  this  experiment  far 
enough ;  every  repetition  would  but  exhibit  the  same  appear- 
ances. 

Lime  combines  with  most  of  the  acids,  to  which  the  carbo- 
nic (as  being  the  weakest)  readily  yields  it;  but  these  combina- 
tions we  shall  have  an  opportunity  of  noticing  more  particular- 
ly hereafter.  It  unites  with  phosphorus,  and  with  sulphur,  in 
their  simple  state;  in  short,  of  all  the  earths,  lime  is  that  which 
nature  employs  most  frequently,  and  niost  abundantly,  in  its  in- 
numerable combinations.  It  is  the  basis  of  all  calcareous  earths 
and  stones ;  we  find  it  likewise  in  the  animal  and  the  vegeta- 
ble creations. 

Emily.  And  in  the  arts  is  not  lime  of  very  great  utility  ? 

Mrs.  B.  Scarcely  any  substance  more  so;  you  know  that  it- 


MAGNESIA.  19$ 

is  a  most  essential  requisite  in  building,  as  it  constitutes  the  ba- 
sis of  all  cements,  such  as  mortar,  stucco,  plaster,  &c. 

Lime  is  also  of  infinite  importance  in  agriculture;  it  lightens 
and  warms  soils  that  are  too  cold  and  compact,  in  consequence 
of  too  great  a  proportion  of  clay. — But  it  would  be  endless  to 
enumerate  the  various  purposes  for  which  it  is  employed  ;  and 
you  know  enough  of  it  to  form  some  idea  of  its  importance  ;  we 
shall,  therefore,  now  proceed  to  the  third  alkaline  earth,  MAG- 
NESIA. 

Caroline.  I  am  already  pretty  well  acquainted  with  that 
earth ;  it  is  a  medicine. 

Mrs.  B.  It  is  in  the  state  of  carbonat  that  magnesia  is  usual- 
ly employed  medicinally;  it  then  differs  but  little  in  appear- 
ance from  its  simple  form,  which  is  that  of  a  very  fine  light 
white  powder.  It  dissolves  in  2000  times  its  weight  of  water, 
but  forms  with  acids  extremely  soluble  salts  It  has  not  so 
great  an  attraction  for  acids  as  lime,  and  consequently  yields 
them  to  the  latter.  It  is  found  in  a  great  variety  of  mineral 
combinations,  such  as  slate,  mica,  and  amianthus,  and  more 
particularly  in  a  certain  lime-stone,  which  has  lately  been  dis- 
covered by  Mr.  Tennant  to  contain  it  in  very  great  quantities. 
It  does  not  attract  and  solidify  water,  like  lime  :  but  when  mix- 
ed with  water  and  exposed  to  the  atmosphere,  it  slowly  absorbs 
carbonic  acid  from  the  latter,  and  thus  loses  its  causticity.  Its 
chief  use  in  medicine  is,  like  that  of  lime,  derived  from  its  read- 
iness to  combine  with,  and  neutralise,  the  acid  which  it  meets 
with  in  the  stomach. 

Emily.  Yet,  you  said  that  it  was  taken  in  the  state  o4*  carbo- 
nat, in  which  case  it  has  already  combined  with  an  acid  ? 

Mrs.  B.  Yes;  but  the  carbonic  is  the  last  of  all  the  acids  in 
the  order  of  affinities;  it  will  therefore  yield  the  magnesia  to 
any  of  the  others.  It  is,  however,  frequently  taken  in  its  caus- 
tic state  as  a  remedy  for  flatulence.  Combined  with  sulphuric 
acid,  magnesia  forms  another  and  more  powerful  medicine,  com- 
monly called  EpKoni  salt. 

Caroline.  And  properly,  sulphat  of  magnesia,  I  suppose  ? 
Pray  why  was  it  ever  called  Kpsorn  salt? 

Mrs.  :?.  Because  there  is  a  spring  in  the  neighbourhood  of 
Epsom  which  contains  this  salt  in  great  abundance. 

The  last  alkaline  earth  which  we  have  to  mention  is  STRON- 
TIAN,  or  STRONTITES,  discovered  by  Dr.  Hope  a  few  years  ago. 
It  so  strongly  resembles  barytes  in  its  properties,  and  is  so  spar- 
ingly found  in  nature,  and  of  so  little  use  in  the  arts,  that  it  will 
not  be  necessary  to  enter  into  any  particulars  respecting  it. 
One  of  the  remarkable  characteristic  properties  of  strontites  is, 


that  its  sails,  when  dissolved  in  spirit  of  wine,  tinge  the  flame  o*' 
a  deep  red,  or  uiood  colour. 


CONVERSATION  XVI. 

ON  ACIDS, 

Mrs.  B.  WE  may  now  proceed  to  the  acids.  Of  the  metallic 
oxyds,  you  have  already  acquired  some  general  notions.  This 
subject,  though  highly  interesting  in  its  details,  is  not  of  suffi- 
cient importance  to  our  concise  view  of  chemistry,  to  he  partic- 
ularly treated  of;  but  it  is  absolutely  necessary  that  you  should 
be  better  acquainted  with-  the  acids,  and  likewise  with  then 
combinations  with  the  alkalies,  which  form  the  triple  com- 
pounds Called  NEUTRAL  SALTS. 

The  class  of  acids  is  characterised  by  very  distinct  proper- 
ties. They  all  change  blue  vegetable  infusions  to  a  red  colour  ; 
they  are  all  more  or  less  sour  to  th»j  taste  ;  and  have  a  general 
tendency  to  combine  with  the  earths,  alkalies,  and  metallic 
oxyds. 

You  have,  I  believe,  a  clear  idea  of  the  nomenclature  by 
'Which  the  base  (or  radical)  of  the  acid,  and  the  various  degrees 
of  acidification,  are  expressed  ? 

Emily.  Yes,  I  think  so;  the  acid  is  distinguished  by  the 
name  of  its  base,  and  its  degree  of  oxydation,  that  is,  the  quanti- 
ty of  oxygen  it  contains,  by  the  termination  of  that  name  in  ous 
oric;  thus  sulphureous  acid  is  that  formed  by  the  smallest 
proportion  of  oxygen  combined  with  sulphur;  sulphuric  acid  is 
that  which  results  from  the  combination  of  sulphur  with  the 
greatest  quantity  of  oxygen. 

Mrs.  B.  A  still  greater  latitude  may,  in  many  cases,  be  al- 
lowed to  the  proportions  of  oxygen  that  can  be  combined  with 
acidificiable  cadicals  ;  for  several  of  these  radicals  are  suscepti- 
ble of  uniting  with  a  quantity  of  oxygen  so  small  as  to  be  insuf- 
ficient to  give  them  the  properties  of  acids  :  in  these  cases, 
therefore,  they  are  converted  into  oxyds.  Such  is  sulphur, 
which  by  exposure  to  the  atmosphere  with  a  degree  of  heat  in- 
adequate to  produce  inflammation,  absorbs  a  small  proportion  of 
oxygen,  which  colours  it  red  or  brewni  This,  therefore,  is  the 
first  degree  of  oxygenation  of  sulphur  ;  the  2d  converts  it  into 
s'ti -ihnrous  acid;  the  3d  into  the  sulphuric  acid  ;  and  4ihly,  if 
found  capable  of  combining  with  a  still  larger  proportion 
of  -  .vygeti,  it  would  then  be  termed  super-oxygenated  sulphur" 
acid. 


ACIDS.  197 

Emily.  Are  these  various  degrees  of  oxygenation  common 
to  all  the  acids  ? 

Mrs.  B.  No  5  they  vary  much  in  this  respect :  some  are  sus- 
;•  piible  of  only  one  degree  of  oxygenation;  others,  of  two,  or 
•.hive;  there  are  but  very  few  that  will  admit  of  more. 

Caroline.  The  modern  nomenclature  must  be  of  immense  ad- 
vantage in  pointing  out  so  easily  the  nature  of  the  acids,  and 
their  various  degrees  of  oxygenation. 

Mrs.  B.  Till  lately  many  of  the  acids  had  not  been  decom- 
posed ;  but  analogy  afforded  so  strong  a  proof  of  their  com- 
pound nature,  that  I  never  could  reconcile  myself  to  classing 
diem  with  the  simple  bodies,  though  this  division  has  been 
adopted  by  several  chemical  writers.  At  present  there  are  on- 
ly the  muriatic  and  the  fluoric  acids,  which  have  not  had  their 
bases  distinctly  separated. 

Caroline.  We  have  heard  of  a  great  variety  of  acids  5  pray 
how  many  are  there  in  all  ? 

Mrs.  B.  I  believe  there  are  reckoned  at  present  thirty-four, 
and  their  number  is  constantly  increasing,  as  the  science  im- 
proves; but  the  most  important,  and  those  to  which  we  shall 
almost  entirely  confine  our  attention,  are  but  few.  I  shall,  how- 
ever, give  you  a  general  view  of  the  whole  ;  and  then  we  shall 
more  particularly  examine  those  that  are  the  most  essential. 

This  class  of  bodies  was  formerly  divided  into  mineral,  ve- 
getable, and  animal  acids,  according  to  the  substances  from 
which  they  were  commonly  obtained. 

Caroline.  That,  I  should  think,  must  have  been  an  excellent 
arrangement ;  why  was  it  altered  ? 

Mrs.  B.  Because  in  many  cases  it  produced  confusion.  In 
which  class,  for  instance,  would  you  place  carbonic  acid  ? 

Caroline.  Now  I  see  the  difficulty.  I  should  be  at  a  loss 
where  to  place  it,  as  you  have  told  us  that  it  exists  in  the  ani- 
mal, vegetable,  and  mineral  kingdoms. 

Emily.  There  would  be  the  same  objection  with  respect  to 
phosphoric  acid,  which,  though  obtained  chiefly  from  bones, 
can  also,  you  said,  be  found  in  small  quantities  in  stones,  and 
likewise  in  some  plants. 

Mrs.  /;.  You  see,  therefore,  the  propriety  of  changing  this 
mode  of  classifica  ion.  These  objections  do  not  exist  in  the 
present  nomenclature ;  for  the  composition  and  nature  of  each 
individual  acid  is  in  some  degree  pointed  out,  instead  of  the 
class  of  bodies  from  which  it  is  extracted;  and,  with  regard  to 
the  more  general  division  of  acids,  they  are  classed  under  these 
three  heads : 

Firs>t,  Acids  of  known  or  supposed  simple  bases,  which  .are 
18* 


193 


ACIDS. 


formed  by  the  union  of  these  bases  with  oxygen.     They 
the  following  : 


The  Sulphuric 
Carbonic 
Nttric 
Phosphoric 
Arsenical 
Tungstenic 
Molybdenic 
Boracic 
Fluoric 
Muriatic 


Acids,  of  known  and  simple  bas<$. 


This  class  comprehends  the  most  anciently  known  and  most 
important  acids.  The  sulphuric,  nitric,  and  nyjriatic  were  for- 
merly, and  are  still  frequently,  called  mineral  acids. 

2dly,  Acids  that  have  double  or  binary  radicals,  and  which 
eonsequently  consist  of  triple  combinations.  These  are  the 
vegetable  acids,  whose  common  radical  is  a  compound  of  hy- 
drogen and  carbon. 

Caroline.  But  if  the  basis  of  all  the  vegetable  acids  be  the 
same,  it  should  form  but  one  acid ;  it  mav  indeed  combine  with 
different  proportions  of  oxygen,  but  the  nature  of  the  acid  must 
be  the  same. 

JvJrs.  Ll.  The  only  difference  that  exists  in  the  basis  of  veget- 
able acids,  is  the  various  proportions  of*  hydrogen  and  carbon 
from  which  they  are  severally  composed.  But  this  is  enough  to 
produce  a  number  of  acids  apparently  very  dissimilar.  That 
the.y  do  not,  however,  differ  essentially,  is  proved  by  their  sus- 
ceptibility of  being  converted  into  each  other,  by  the  addition 
or  subtraction  of  a  portion  of  hydrogen  or  of  carbon.  The 
sanies  of  these  acids  are, 

The  Acetic 
Oxalic 
Tartarous 
Citric 

Acids,  of  double  bases,  being  of  vegeta- 
J\ucous  bleorgin. 

Benzoic 
Sue  time 
Camphoric 
Suberic 


ACIOS.  199 

The  3d  class  of  acids  consists  of  those  which  have  triple  rad- 
icals, and  are  therefore  ot  a  still  more  compound  nature.  Tlfts 
class  comprehends  the  animal  acids,  which  are, 


The  Lactic  7 
Prussi-c 
Formic 
Bombic 
Sebacic 
Zoonic 
Lithic 


>  Acids,  of  triple  bases,  or  animal  acids. 


•  I  have  given  you  this  summary  account  or  enumeration  of 
the  acids,  as  you  may  find  it  more  satisfactory  to  have  at  once 
an  outline  or  a  general  notion  of  the  extent  of  the  subject ;.  but 
we  shall  now  confine  ourselves  to  the  first  class,  which  requires 
our  more  immediate  attention;  and  defer  the  few  remarks 
which  we  shall  have  to  make  on  the  others,  till  we  treat  of  the 
chemistry  of  the  animal  and  vegetable  kingdoms. 

The  acids  of  simple  and  known  radicals  are  all  capable  of 
being  decomposed  by  combustible  bodies,  to  which  they  yield 
their  oxygen.  11',  for  instance,  1  pour  a  drop  of  sulphuric  acid 
on  this  piece  of  iron,  it  will  produce  a  spot  of  rust,  you  know 
what  that  is  ? 

Caroline.  Yes;  it  is  an  oxyd,  formed  by  the  oxygen  of  the 
acid  combining  with  the  iron. 

Mrs.  B.  In  this  case  you  see  the  sulphur  deposits  the  oxy- 
gen by  which  it  was  acidified  on  the  metal.  And  again,  if  we 
pour  someacid  on  a  compound  combustible  substance,  (we  shall 
try  it  on  this  piece  of  wood,)  it  will  combine  with  one  or  more 
of  the  constituents  of  that  substance,  and  occasion  a  decomposi- 
tion. 

Emily.  It  has  changed  the  colour  of  the  wood  to  black.  How 
is  that  ? 

J\-:'rs.  tt.  The  oxygen  deposited  by  the  acid  has  burnt  it ; 
you  know  that  wood  in  burning  becomes  black  before  it  is  re- 
duced to  ashes.  Whether  it  derives  the  oxygen  which  burns  it 
from  the  atmosphere,  or  from  any  other  source,  the  chemical 
effect  on  the  wood  is  the  same.  In  the  case  of  real  combustion, 
wood  becomes  black,  because  it  is  reduced  to  the  state  of  char- 
coal by  the  evaporation  of  its  other  constituents.  But  can  you 
tell  me  the  reason  wuy  wood  turns  black  when  burnt  by  the 
application  of  an  acid  ? 

Caroline.  First,  tell  me  what  are  the  ingredients  of  wood  ? 


£00'  ACIDS. 

Mrs.  B.  Hydrogen  and  carbon  are  the  chief  constitutes  of 
wood,  as  of  all  other  vegetable  substances. 

Caroline.  Well,  then,  I  suppose  that  the  oxygen  of  the  acid 
combines  with  the  hydrogen  of  the  wood,  to  form  water  ;  and 
that  the  carbon  of  the  wood,  remaining  alone,  appears  of  its 
usual  black  colour. 

Mrs.  B.  Very  well  indeed,  my  dear ;  that  is  certainly  the 
most  plausible  explanation. 

Caroline.  Would  not  this  be  a  good  method  of  making  char- 
coal ? 

Mrs.  B.  It  would  be  an  extremely  expensive,  and,  I  believe, 
very  imperfect  method  ;  for  the  action  of  the  acid  on  the  wood, 
and  the  heat  produced  by  it,  are  far  from  sufficient  to  deprive 
the  wood  of  all  its  evaporable  parts. 

Caroline.  What  is  the  reason  that  vinegar,  lemon,  and  the 
acid  of  fruits,  do  not  produce  this  effect  on  wood  ? 

Mrs.  H.  They  are  vegetabe  acids,  whose  bases  are  composed 
of  hydrogen  and  carbon  ;  the  oxygen,  therefore,  will  not  be  dis- 
posed to  quit  this  radical,  where  it  is  already  united  with  hydro- 
gen. The  strongest  of  these  may,  perhaps,  yield  a  little  of 
their  oxygen  to  the  wood,  and  produce  a  stain  upon  it ;  but  the 
carbon  will  not  be  sufficiently  uncovered  to  assume  its  black 
colour.  Indeed,  the  several  mineral  acids  themselves  possess 
chis  power  of  charring  wood  in  very  different  degrees. 

Emily.  Cannot  vegetable  acids  be  decomposed,  by  any  com- 
bustibles ? 

Mrs.  B.  N-9  ;  because  their  radical  is  composed  of  two  sub- 
stances which  have  a  greater  attraction  for  oxygen  than  any 
known  body. 

Caroline.  And  are  those  strong  acids,  which  burn  and  de- 
compose wood,  capable  of  producing  similar  effects  on  the 
skin  and  flesh  of  animals  ? 

,  \lrs.  B.  Yes  ;  all  the  mineral  acids,  and  one  of  them  more 
especially,  possess  powerful  caustic  qualities.  They  actually 
corrode  and  destroy  the  skin  and  flesh  ;  but  they  do  not  produce 
upon  these  exactly  the  same  alteration  they  do  on  wood,  proba- 
bly because  there  is  a  great  proportion  of  nitrogen  and  other 
substances  in  animal  matter,  which  prevents  the  separation  of 
carbon  from  being  so  conspicuous. 


«5>F  SULPHURIC  AND  SULPHUREOUS  ACIDS.  20i 


CONVERSATION  XVII. 

Of  THE  SULPHURIC  AND  PHOSPHORIC  ACIDS;  Oil  THE 
COMBINATION  OF  OXYGEN  VVI  TH  SULPHUR  AND  PHOS- 
PHORUS ;  AND  OF  THE  SULPHA  FS  AND  PHOSPH  \  TS. 

Mrs.  B.  IN  addition  to  the  general  survey  which  we  have 
takep  of  acids,  I  think  you  will  find  it  interesting  to  examine 
individually  a  tew  of  the  most  important  of  them,  and  like- 
wise some  of  their  principal  combination  with  the  alkalies,  al- 
kaline earths,  and  metals.  The  first  of  the  acids,  in  point  of 
importance,  is  the  SULPHURIC,  formerly  called  oil  of  vitriol. 

Caroline.  I  have  known  it  a  long  time  by  that  name,  but 
had  no  idea  that  it  was  the  same  fluid  as  sulphuric  acid.  What 
resemblance  or  connection  can  there  be  between  oil  of  vitriol 
and  this  acid  ? 

Mrs.  B.  Vitrol  is  the  common  name  for  sulphat  of  iron,  a 
salt  which  is  formed  by  the  combination  of  sulphuric  acid  and 
iron;  the  sulphuric  acid  was  formerly  obtained  by  distillation 
from  this  salt,  and  it  very  naturally  received  its  name  from  the 
substance  which  afforded  it. 

Caroline.  But  it  is  still  usually  called  oil  of  vitirol  ? 

Mrs.  B.  Yes  ;  a  sufficient  length  of  time  has  not  yet  elap- 
sed, since  the  invention  of  the  new  nomenclature,  for  it  to  be 
generally  disseminated  ;  but,  as  it  is  adopted  by  all  scientific 
chemists,  there  is.  every  reason  to  suppose  that  it  will  gradu- 
ally beco.ne  universal.  When  I  received  this  bottle  from  the 
chemists,  oil  of  vitriol  was  inscribed  on  the  label ;  but,  as  1 
knew  you  were  very  punctilious  in  regard  to  the  nomenclature, 
I  changed  it,  and  substituted  the  words  sulphuric  acid. 

Emily.  This  acid  has  neither  colour  nor  smell,  but  it  ap- 
pears much  thicker  than  water. 

Mrs.  B.  It  is  nearly  twice  as  heavy  as  water,  and  has,  you 
see,  an  oily  consistence. 

Caroline.  And  it  is  probably  from  this  circumstance  that  it 
has  been  called  an  oil,  for  it  can  have  no  real  claim  to  that 
name,  as  it  does  not  contain  either  hydrogen  or  carbon,  which 
are  the  essential  constituents  of  oil. 

Mrs.  B.  Certainly ;  and  therefore  it  would  be  the  more  ab- 
surd to  retain  a  name  which  owed  its  origin  to  such  a  mistaken 
analogy. 

Sulphuric  acid,  in  its  purest  state,  would  probably  be  a  con- 
crete substance,  but  its  attraction  for  water  is  such,  that  it  is  im- 
possible to  obtain  that  acid  perfectly  free  from  it  j  it  is,  there- 


202  OP  THE  SULPHURIC 

fore,  always  seen  in  a  liquid  form,  such  as  you  here  find  it, 
One  of  the  rrnst  striking  properties  of  sulphuric  acid  is  that  ot 
evolving  a  considerable  quantity  of  heat  when  mixed  with  wa- 
ter; this  I  have  already  shown  you. 

Emily.  Yes,  I  recollect  it ;  but  what  was  the  degree  of  heat 
produced  by  that  mixture  ? 

Mrs.  B.  The  thermometer  may  be  raised  by  it  to  300  de- 
grees, which  is  considerably  above  the  temperature  of  boiling 
water. 

Caroline.  Then  water  might  be  made  to  boil  in  that  mix- 
ture? 

Mrs.  B.  Nothing  more  easy,  provided  that  you  employ  suf- 
ficient quantities  of  acid  and  of  water,  and  in  the  due  propor- 
tions. The  greatest  heat  is  produced  by  a  mixture  of  one  part 
of  water  to  four  of  the  acid  :  we  shall  make  a  mixture  of  these 
proportions,  and  immerse  in  it  this  thin  glass  tube,  which  is  full 
of  water. 

Caroline.  The  vessel  feels  extremely  hot,  but  the  water  does 
not  boil  yet. 

Mrs.  B.  You  must  allow  some  time  for  the  heat  to  penetrate 
the  tube,  and  raise  the  temperature  of  the  water  to  the  boiling 
point — 

Caroline.  Now  it  boils — and  with   increasing  violence. 

Mrs.  B.  But  it  will  not  continue  boiling  long  ;  for  the  mix- 
ture gives  out  heat  only  while  the  particles  of  the  water  and 
the  acid  are  mutually  penetrating  each  other:  as  soon  as  the 
new  arrangement  of  those  particles  is  effected,  the  mixture  will 
gradually  cool,  and  the  water  return  to  its  former  temperature. 

You  have  seen  the  manner  in  which  sulphuric  acid  decompo- 
ses all  combustible  substances,  whether  animal,  vegetable,  or 
mineral,  and  burns  them  by  means  of  its  oxygen  ? 

Caroline.  I  have  very  unintentionally  repeated  the  experi- 
ment on  my  gown,  by  letting  a  drop  of  the  acid  fall  upon  it,  and 
it  has  made  a  stain,  which,  I  suppose,  will  never  wash  out. 

Mrs.  B.  No,  certainly  ;  for  before  you  can  put  it  into  water, 
the  spot  will  become  a  hole,  as  the  acid  has  literally  burnr  the 
muslin. 

Caroline.  So  it  has  indeed  !  Well,  I  will  fasten  the  stopper, 
and  put  the  bottle  away,  for  it  is  a  dangerous  substance, — Oh, 
now  I  have  done  worse  still,  for  I  have  spilt  some  on  «v  hand  ! 

Mrs.  B.  It  is  then  burned,  as  well  as  your  gown,  tor  you 
know  thelt  oxygen  destroys  animal  as  well  as  vegetable  matters; 
and,  as  far  as  the  decomposition  of  the  skin  of  your  finger  is 
effected,  there  is  no  remedy .;  but  by  washing  it  immediately  in 
water,  you  will  dilute  the  acid,  and  prevent  any  further  injury. 


AND  SULPHUREOUS  ACIDS.  203 

Caroline.  It  feels  extremely  hot,  I  assure  you. 

JV/rs.  B.  You  have  now  learned,  by  experience,  how  cau- 
tiously this  acid  must  be  used.  You  will  soon  become  acquain- 
ted with  another  acid,  the  nitric,  which,  though  it  produces  less 
heat  on  the  skin,  destroys  it  still  quicker,  and  makes  upon  it  an 
indelible  stain.  You  should  never  handle  any  substances  of 
this  kind,  without  previously  dipping  your  fingers  in  water, 
which  will  weaken  their  caustic  effects.  But,  since  you  will 
not  repeat  the  experiment,  I  must  put  in  the  stopper,  for  the 
acid  attracts  the  moisture  from  the  atmosphere,  which  would  de- 
stroy its  strength  and  purity. 

Emily.  Pray,  how  can  sulphuric  acid  be  extracted  from  sul- 
phat  of  iron  by  distillation  ? 

Mrs.  B.  The  process  of  distillation,  you  know,  consists  in 
separating  substances  from  one  another  by  means  of  their  dif- 
ferent degrees  of  volatility,  and  by  the  introduction  of  a  new 
chemical  agent,  caloric.  Thus,  if  sulphat  of  iron  be  exposed 
in  a  retort  to  a  proper  degree  of  heat,  it  will  be  decomposed, 
and  the  sulphuric  acid  will  be  volatilised. 

Emily.  But  now  that  the  process  of  forming  acids  by  the 
combustion  of  their  radicals  is  known,  why  should  not  this 
method  be  used  for  making  sulphuric  acid  ? 

Mrs.  B.  This  is  actually  done  in  most  manufactures;  but 
the  usual  method  of  preparing  sulphuric  acid  does  not  consist 
in  burning  the  sulphur  in  oxygen  gas  (as  we  formerly  did  by  the 
way  of  experiment,)  but  in  heating  it  together  with  another 
substance,  nitre,  which  yields  oxygen  in  sufficient  abundance  to 
render  the  combustion  in  common  air  rapid  and  complete. 

Caroline.  This  substance,  then,  answers  the  same  purpose 
as  oxygen  gas  ? 

Jtirs.  B.  Exactly.  In  manufactures  the  combustion  is  per- 
formed in  a  leaden  chamber,  with  water  at  the  bottom,  to  re- 
ceive the  vapour  and  assist  its  condensation.  The  combustion 
is,  however,  never  so  perfect  but  that  a  quantity  of  sulphure- 
ous acid  is  formed  at  the  same  time  ;  for  you  recollect  ihat  the 
sulphureous  acid  according  to  the  chemical  nomenclature,  dif- 
fers from  the  sulphuric  only  by  containing  less  oxygen. 

From  its  own  powerful  properties,  and  from  the  various  com- 
binations into  which  it  enters,  sulphuric  acid  is  of  great  impor- 
tance in  many  of  the  arts. 

It  is  used  also  in  medicine  in  a  state  of  great  dilution;  for 
were  it  taken  internally,  in  a  concentrated  state,  it  would  prove 

:son. 
o,,,  .,t.,oii  would  bum  the  throat  and  stomach. 


204  OF  THE  SULPURIC  AND  SULPHUREOUS  ACIDS. 

Mrs.  B.  Can  you  think  of  any  thing  that  would  prove  aii 
antidote  to  this  poison  ? 

Caroline.  A  large  draught  of  water  to  dilute  it. 

Mrs.  B.  That  would  certainly  weaken  the  caustic  power  o? 
the  acid,  but  it  would  increase  the  hrat  to  an  intolerable  degree. 
Do  you  recollect  nothing  that  wpuld  destroy  its  deleterious  prop- 
erties more  effectually  ? 

Emily.  An  alkali  might,  by  combining  with  it  ;  but,  then,  a 
pure  alkali  is  itfelf  a  poison,  on  account  of  its  causticity. 

Mrs.  B.  There  is  no  n  ecessity  that  the  alkali  should  be  cans- 
tic.  Soap,  in  which  it  is  combined  with  oil ;  or  magnesia,  ei- 
ther in  the  state  of  carbonat,  or  mixed  with  water,  would  prove 
the  best  antidotes. 

Emily.  In  those  cases  then,  I  suppose,  the  potash  and  the 
magnesia  would  quit  their  combinations  to  form  salts  with  the 
sulphuric  acid  ? 

Mrs.  B.  Precisely. 

We  may  now  make  a  few  observations  on  the  sulphureows 
acid,  which  we  have  found  to  be  the  product  of  sulphur  slowly 
and  imperfectly  burnt.  This  acid  is  distingusshed  by  its  pun- 
gent smell,  and  its  gaseous  foim. 

Caroline.  Its  aeriform  state  is,  I  suppose,  owing  to  the  smal- 
ler proportion  of  oxygen,  which  renders  it  lighter  than  sulphu- 
nc  acid  ? 

Mrs.  B.  Probably  ;  for  by  adding  oxygen  to  the  weaker  ac- 
id, it  may  be  converted  into  the  stronger  kind.  But  this 
change  of  state  may  also  be  connected  with  a  change  of  affiiii- 
ty  with  regard  to  caloric. 

Emily.  And  may  sulphureous  acid  be  obtained  from  sulphu- 
ric acid  by  a  diminution  of  oxygen  ? 

Mrs.  B.  Yes;  it  can  be  done  by  bringing  any  combustible 
substance  in  contact  with  the  acid.  This  decomposition  is 
most  easily  performed  by  some  of  the  metals;  these  absorb  a 
portion  of  the  oxygen,  from  the  sulphuric  acid,  which  is  thus 
converted  into  the  sulphureous,  and  flies  off  in  its  gaseous 
form. 

Caroline.  And  cannot  the  sulphureous  acid  itself  be  decom- 
posed and  reduced  to  sulphur  ? 

Mrs.  B.  Yes  ;  if  this  gas  be  heated  in  contact  with  charcoal, 
the  oxygen  of  the  gas  will  combine  with  it,  and  the  pure  sui-. 
phur  is  regenerated. 

Sulphureous  acid  is  readily  absorbed  by  water  ;  and  in  this 
liquid  state  it  is  found  particularly  useful  in  bleaching  linen  and 
woollen  cloths,  arid  is  much  used  in  manufactures  for  those  pur- 
poses, J  can  show  you  its  effect  in  destroying  colours,  by  ta 


OP  THE  SULPHATS.  205 

king  out  vegetable  stains — I  think  I  see  a  spot  on  your  gown, 
Emily,  on  which  we  may  try  the  experiment. 

Emihf.  It  is  the  stain  of  mulberries ;  but  I  shall  be  almost 
afraid  of  exposing  my  gown  to  the  experiment,  after  seeing  the 
effect  which  the  sulphuric  acid  produced  on  that  of  Caroline — • 

J.r*.  b.  There  is  no  such  danger  from  the  sulphureous;  but 
the  experiment  must  be  made  with  great  caution,  for  during  the 
formation  of  sulphureous  acid  by  combustion,  there  is  always 
some  sulphuric  produced. 

Caroline.  But  where  is  your  sulphureous  acid  ? 

Mrs.  B.  We  may  easily  prepare  some  ourselves,  simply  by 
burning  a  match  ;  we  must  first  wet  the  stain  with  water,  and 
now  hold  it  in  this  way,  at  a  little  distance,  over  the  lighted 
match  :  the  vapour  that  arises  from  it  is  sulphureous  acid,  and 
the  stain,  you  see,  gradually  disappears. 

Emily.  I  have  frequently  taken  out  stains  by  this  means, 
without  understanding  the  nature  of  the  process.  But  why  is 
it  necessary  to  wet  the  stain  before  it  is  exposed  to  the  acid 
fumes  ? 

Mrs.  B.  The  moisture  attracts  and  absorbs  the  sulphureous 
acid  $  and  it  serves  likewise  to  dilut?  any  particles  of  sulphu- 
ric acid  which  might  injure  the  linen. 

Sulphur  is  susceptible  of  a  third  combination  with  oxygen,  in 
which  the  proportion  of  the  latter  is  too  small  to  render  the 
sulphur  acid.  It  acquires  this  slight  oxygenation  by  mere  ex- 
posure to  the  atmosphere,  without  any  elevation  of  tempera- 
ture :  in  this  case,  the  sulphur  does  not  change  its  natural  form, 
but  is  only  discoloured,  being  changed  to  red  or  brown;  and  in 
this  state  it  is  an  oxyd  of  sulphur. 

Before  we  take  leave  of  the  sulphuric  acid,  we  shall  say  a  few 
words  of  its  principal  combinations.  It  unites  with  all  the  al- 
kalies, alkaline  earths  and  metals,  to  form  compound  salts. 

Caroline.  Pray,  give  me  leave  to  interrupt  you  for  a  mo- 
ment :  you  have  never  mentioned  any  other  salts  than  the 
compound  or  neutral  salts ;  is  there  no  other  kind  ? 

Mrs.  B.  The  term  salt  has  been  used,  from  time  immemo- 
rial, as  a  kind  of  general  name  for  any  substance  that  has  sa- 
vour, odour,  is  soluble  in  water,  and  crystallisable,  whether  it 
be  of  an  acid,  an  alkaline,  or  compound  nature;  but  the  com- 
pound salts  alone  retain  that  appellation  in  modern  chemistry. 

The  most  important  of  the  salts,  formed  by  the  combinations 
of  the  sulphuric  acid,  are,  first,  sulphat  of  potash,  formerly 
called  sal  polycrest :  this  is  a  very  bitter  salt,  much  used  in 
medicine ;  it  is  found  in  the  ashes  of  most  vegetables,  but  it  may 
be  prepared  artificially  by  the  immediate  combination  of  sut 

19 


206  OP  THE  SULPHATS- 

phuric  acid  and  potash.  This  salt  is  easily  soluble  in  boiling 
water.  Solubility  is,  indeed,  a  property  common  to  all  salts  ; 
and  they  always  produce  cold  in  melting. 

Emily.  That  must  be  owing  to  the  caloric  which  they  ab- 
sorb in  passing  fiom  a  solid  to  a  fluid  form. 

Airs.  B.  That  is,  certainly,  the  most  probable  explanation. 

Sulphat  of  soda,  commonly  called  Glauber's  salt,  is  another 
medicinal  salt,  which  is  still  more  bitter  than  the  preceding. 
We  must  prepare  some  of  these  compounds,  that  you  may  ob- 
serve the  phenomena  which  take  place  during  their  formation. 
We  need  only  pour  some  sulphuric  acid  over  the  soda  which  I 
have  put  into  this  glass. 

Caroline.  What  an  amazing  heat  is  disengaged  ! — I  thought 
you  said  that  cold  was  produced  by  the  melting  of  salts  ? 

Mrs.  B.  But  you  must  observe  that  we  are  now  making,  not 
melting'  a  salt.  Heat  is  disengaged  during  the  formation  of 
compound  salts,  and  a  faint  light  is  also  emitted,  which  may 
sometimes  be  perceived  in  the  dark. 

Emily.  And  is  this  heat  and  light  produced  by  the  union  of 
the  two  opposite  electricities  of  the  alkali  and  the  acid  ? 

Mrs.  B.  No  doubt  it  is,  if  that  theory  be  true. 

Caroline.  The  union  of  an  acid  a;id  an  alkali  is  then  an  ac- 
tual combustion  ? 

Mrs.  B.  Not  precisely,  though  there  is  certainly  much  anal- 
ogy in  these  processes. 

Caroline,  Will  this  sulphat  of  soda  become  solid  ? 

Mrs.  B.  We  have  not,  I  suppose,  mixed  the  acid  and  the  al- 
kali in  the  exact  proportions  that  are  required  for  the  formation 
of  the  salt,  otherwise  the  mixture  would  have  been  almost  im- 
mediately changed  to  a  solid  mass  ;  but,  in  order  to  obtain  it 
In  crystals,  as  you  see  it  in  this  bottle,  it  would  be  necessary 
first  to  dilute  it  with  water,  and  afterwards  to  evaporate  the 
water,  during  which  operation  the  salt  would  gradually  crystal- 
lise. 

Caroline.  But  of  what  use  is  the  addition  of  water,  if  it  is 
afterwards  to  be  evaporated  ? 

Mrs.  b.  When  suspended  in  water,  the  acid  and  the  alkali 
:ire  more  at  liberty  to  act  on  each  other,  their  union  is  more 
complete,  and  the  salt  assumes  the  regular  form  of  crystals  du- 
ring the  slow  evaporation  of  its  solvent 

Sulphat  of  soda  liquefies  by  heat,  and  effloresces  in  the  air. 

Emily.  Pray  what  is  the  meaning  of  the  word  effloresces? 
I  do  not  recollect  your  having  mentioned  it  before. 

Mrs.  />.  A  salt  is  said  to  effloresce  when  it  loses  its  water  of 
crystallisation  on  being  exposed  to  the  atmosphere,  and  is  thus 


jf  THE 

gradually  converted  iuto  a  dry  pow:ler  :  you  may  observe  that 
these  crystals  of  sulphat  of  soda  are  far  from  possessing  the 
transparency  which  belongs  to  their  crystalline  state;  they  are 
covered  with  a  white  powder,  occasioned  by  their  having  been 
exposed  to  the  atmosphere,  which  has  deprived  their  surface  of 
its  lustre,  by  absorbing  its  water  of  crystallisation.  Salts  are, 
ai  general,  either  efflorescent  or'deliquescent  ;  this  latter  prop- 
erty is  precisely  the  reverse  of  the  former  ;  that  is  to  say,  de- 
liquescent salts  absorb  water  from  the  atmosphere,  and  are 
snoistened  and  gradually  melted  by  it.  Muriat  of  lirne  is  an 
instance  of  great  deliquescence. 

Emily.  But  are  there  no  salts  that  have  the  same  degiee  of 
attraction  for  water  as  the  atmosphere,  and  that  will  conse- 
quently not  be  affected  by  it  ? 

Mrs.  B.  Yes;  there  are  many  such  salts,  as,  for  instance, 
common  salt,  sulphat  of  magnesia,  and  a  variety  of  others. 

Sulphat  of  lime  is  very  frequently  met  with  in  nature,  and 
constitutes  the  well-known  substance  called  gypsum,  or  plaster 
of  Parts. 

Sulphat  of  magnesia,  commonly  called  Epsom  salt,  is  ano- 
ther very  bitter  medicine,  which  is  obtained  from  sea-water  and 
from  several  springs,  or  may  be  prepared  by  the  direct  combi- 
nation of  its  ingredients. 

We  have  formerly  mentioned  sulphat  of  alumine  as  consti- 
tuting the  common  alum  ;  it  is  found  in  nature  chiefly  in  the 
neighbourhood  of  volcanoes,  and  is  particularly  useful  in  the 
arts,  from  its  strong  astringent  qualities.  It  is  chiefly  employed 
by  dyers  and  calico-printers,  to  fix  colours  ;  and  is  used  also  in 
the  manufacture  of  some  kinds  of  leather. 

Sulphuric  acid  combines  also  with  the  metals. 

Caroline.  One  of  these  combinations,  Sulphat  of  iron,  we 
are  already  w<jll  acquainted  with. 

Mrs.  B.  That  is  the  most  important  metallic  salt  formed  by 
sulphuric  acid,  and  the  only  one  that  we  shall  here  notice.  It 
is  of  great  use  in  the  arts  ;  and,  in  medicine,  it  affords  a  very 
valuable  tonic  :  it  is  of  this  salt  that  most  of  those  preparations 
called  steel  medicines  are  composed. 

Caroline.  But  does  any  carbon  enter  into  these  compositions 
to  form  steei  ? 

Mrs.  B.  Not  an  atom  :  they  are,  therefore,  very  improperly 
called  steel  :  but  it  is  the  vulgar  appellation;  and  medical  meft 
themselves  often  comply  with  the  general  custom. 

Sulphat  of  iron  may  be  prepared,  as  you  have  seen,  by  dis- 
solving iron  in  sulphuric  acid  ;  but  it  is  generally  obtained 
Jro.m  the  natural  production  called  Pyrites,  which  being  a  sul- 


208 


•OP  THE  SULFHATS. 


phuret  of  iron,  requires  only  exposure  to  the  atmosphere  to  be 
oxydaied,  in  order  to  form  the  salt  ;  this,  therefore,  is  much  the 
most  easy  way  of  procuring  it  on  a  large  scale. 

Emily.  I  a.n  surprised  to  find  that  both  acids  and  compound 
salts  are  generally  obiai iied  from  their   various   combinations, 
^rather  than  from  ihe  immediate  union  of  their  ingredients. 

Mrs.  B.  Were  the  simple  bodies  always  at  hand,  their  com- 
binations would  natur-dlly  be  the  most  convenient  method  of 
forming  compounds;  but  you  must  consider  that,  in  most  in- 
stances, ihere  is  great  difficulty  and  expense  in  obtaining  the 
simple  ingredients  from  their  combinations;  it  is,  therefore  of- 
ten more  expedient  to  procure  compounds  from  the  decomposi- 
tion of  other  compounds.  But,  to  return  to  the  sulphat  of  iron. 
—There  is  a  certain  vegetable  acid  called  Gallic  add,  which 
has  the  remarkable  property  of  precipitating  this  salt  black — I 
shall  pour  a  few  drops  of  the  gallic  acid  into  this  solution  of  sul- 
phat of  iron — 

Caroline.  It  is  become  as  black  as  ink  ! 

Mrs.  B.  And  it  is  ink  in  reality.  Common  writing  ink  is  a 
precipitate  of  sulphat  of  iron  by  "gallic  acid;  the  black  colour 
is  owing  to  the  formation  of  gallar  of  iron,  which  being  insolu- 
ble, renviins  suspended  in  the  fluid. 

This  arid  has  also  the  property  of  altering  the  colour  of  iron 
in  its  metallic  state.  You  may  frequently  see  its  effect  on  the 
blade  of  a  kniie,  that  has  been  used  to  cut  certain  kinds  of 
fruits. 

Caroline.  True;  and  that  is,  perhaps,  the  reason  that  a  sil- 
ver knife  is  preferred  to  cut  fruits;  the  gallic  acid,  I  suppose, 
does  not  act  upon  silver. — Is  this  acid  found  in  all  fruits  ? 

Mrs.  B.  It  is  contained,  more  or  less,  in  the  rind  of  cnost 
fruits  and  roots,  especially  the  radish,  which, -if  scraped  with  a 
steel  or  iron  knife,  has  its  bright  red  colour  changed  to  a  deep 
purple,  the  knife  being  at  the  same  time  blackened.  But  the 
vegetable  substance  in  which  the  gallic  acid  most  abounds  is 
nutgall,  a  kind  of  excrescence  that  grows  on  oaks,  and  from 
which  the  acid  is  commonly  obtained  for  its  various  purposes. 

M-'s.  '3.  W*i  n;nv  come  to  the  PHOSPHORIC  ami  PHOSPHOROUS 
ACIDS.  In  treating  of  phosphorus,  you  have  seen  how  these 
acids  may  be  obtained  from  it  by  combustion  ? 

Emily  YXs ;  but  I  should  be  much  surprised  if  it  was  the 
usual  method  of  obtaining  them,  since  it  is  so  very  difficult  to 
procure  phosphorus  in  its  pure  state. 

Mrs.  You  are  right,  my  dear ;  the  phosphoric  acid,  for 
general  purposes,  is  extracted  from  bones,  in  which  it  is  contain 


OF  THE  NITRIC  AND  NITROUS  ACIDS.  209 

e<j  in  the  state  of  phosphat  of  lime  ;  from  this  salt  the  phos- 
phoric acid  is  separated  by  means  of  the  sulphuric,  which  com- 
bines with  the  lime*  In  its  pure  state,  phosphoric  acid  is  either 
liquid  or  solid,  according  to  its  degree  of  concentration. 

Among  the  salts  formed  by  this  acid,  phosphat  of  lime  is 
the  only  one  that  affords  much  interest ;  and  this,  we  have  al- 
ready observed,  constitutes  the  basis  of  all  bones.  It  is  also 
found  in  very  small  quantities  in  some  vegetables. 


CONVERSATION  XVIII. 

OF  THE  NITRIC  AND  CARBONIC  ACIDS  ;  OR  THE  COM- 
BINATIONS OF  OXYGEN  WITH  NITKOGEN  AND  CAR- 
BON; AND  OF  THE  Nl  FilATS  AND  CARBONA  PS. 

Mrs.  B.  I  AM  almost  afraid  of  introducing  the  subject  of  the 
NITRIC  ACID,  as  I  am  sure  that  I  shall  be  blamed  by  Caroline 
for  not  having  made  her  acquainted  with  it  before. 

Caroline.  Why  so,  Mrs.  B.  ? 

Mrs.  B.  Because  you  have  long  known  its  radical,  which  is 
nitrogen  or  azote;  and  in  treating  of  that  element,  I  did  not  ev- 
en hint  that  it  was  the  basis  of  an  acid. 

Caroline.  And  what  could  be  your  reason  for  not  mention- 
nig  this  acid  sooner  ? 

Mrs.  B.  I  do  not  know  whether  you  will  think  the  reason 
sufficiently  good  to  acquit  me  ;  but  the  omission,  I  assure  you, 
did  not  proceed  from  negligence.  You  may  recollect  that  ni- 
trogen was  one  of  the  first  simple  bodies  which  we  examined  i 
you  were  then  ignorant  of  the  theory  of  combustion,  which  I 
believe  was,  for  the  first  time,  mentioned  in  that  lesson  ;  and 
therefore  it  would  have  been  in  vain,  at  that  time,  to  have  at- 
tempted to  explain  the  nature  and'  formation  of  acids. 

Caroline.  I  wonder,  however,  that  it  never  occurred  to  us  to 
enquire  whether  nitrogen  could  be  acidified ;  for,  as  we  knew 
it  was  classed  among  the  combustible  bodies,  it  was  natural  to 
suppose  that  it  might  produce  an  acid. 

Mrs.  B.  That  is  not  a  necessary  consequence :  for  it  might 
combine  with  oxygen  only  in  the  degree  requisite  to  form  an 
oxyd.  But  you  will  find  that  nitrogen  is  susceptible  of  various 
degrees  of  oxygenation,  some  of  which  convert  it  merely  into 
an  oxyd,  and  others  give  it  all  the  acid  properties. 

The  acids,  resulting  from  the  combination  of  oxygen  and  ni- 
19* 


210 


OF  THE  MTfilL 


trogen,  are  called  the  NITROUS  and  NITRIC  acids.  We  will  be 
gin  with  the  NITRIC,  in  which  nitrogen  is  in  the  highest  state  of 
OK.ypnation.  This  acid  naturally  exists  in  the  form  of  gas ; 
b.u  is  so  very  soluble  in  water,  and  has  so  great  an  affinity  for  it' 
that  one  grain  of  water  will  absorb  and  condense  ten  grains  of 
acid  gas,  and  form  the  limpid  fluid  which  you  see  in  this  bottle, 

Caroline.  What  a  strong  offensive  smell  it  has  ! 

Mrs.  Ji.  This  acid  contains  a  greater  abundance  of  oxygen 
than  any  other,  but  it  retains  it  with  very  little  force. 

Emily.  Then  it  must  be  a  powerful  caustic,  both  from  the 
facility  with  which  it  parts  with  its  oxygen,  and  the  quantity 
which  it  affords  ? 

Mrs.  B.  Very  well,  Emily  ;  both  cause  and  effect  are  exact- 
ly such  as  you  describe :  nitric  acid  burns  and  destroys  all  kinds 
of  organized  matter.  It  even  sets  fire  to  some  of  the  most 
combustible  substances. — We  shall  pour  a  little  of  it  over  this 
piece  of  dry  warm  charcoal* — you  see  it  inflames  it  immedi- 
ately ;  it  would  do  the  same  with  oil  of  tupentine,  phosphorus, 
and  several  other  very  combustible  bodies.  This  shows  you 
how  easily  this  acid  is  decomposed  by  combustible  bodies,  since 
these  effects  must  depend  upon  the  absorption  of  its  oxygen. 

JNitric  acid  has  been  used  in  the  arts  from  time  immemori- 
al, but  it  is  only  within  these  twenty-five  years  that  its  chemical 
nature  has  been  ascertained.  The  celebrated  Mr.  Cavendish  dis- 
covered that  it  consisted  of  about  10  parts  of  nitrogen  and  25 
of  oxygen.t  These  principles,  in  the  gaseous  state,  combine  at 
a  high  temperature ;  and  this  may  be  effected  by  repeatedly 
passing  the  electrical  spark  through  a  mixture  of  the  two  gases. 

Emily.  The  nitrogen  and  oxygen  gases,  of  which  the  atmos- 
phere is  composed,  do  not  combine,  I  suppose,  because  their 
temperature  is  not  sufficiently  elevated  ? 

Caroline.  But  in  a  thunder-storm,  when  the  lightning  re- 
peatedly passes  through  them,  may  it  not  produce  nitric  acid  ? 
W»  should  be  in  a  strange  situation,  if  a  violent  storm  should  at 
once  convert  the  atmosphere  into  nitric  acid. 

Mrs.  B.  There  is  no  danger  of  it,  my  dear ;  the  lightning 

*  To  inflame  charcoal,  a  stronger  acid  than  that  sold  at  the  shops  is 
necessary.  The  experiment,  with  ol.  turpentine  and  phosphorus,  suc- 
ceeds, if  about  a  sixth  part  ofsuiph.  acid  is  added  to  the  nitric  acid. 
The  experiment  with  the  turpentine  requires  caution.  The  vial  con- 
taining the  acid  must  be  tied  to  a  stick,  a  yard  or  two  long,  the  opera- 
tor pouring  it  into  a  small  quantity  of  the  turpentine  standing  at  a 
distance.  C. 

t  The  proportion  stated  by  Sir  H.  Davy,  in  his  Chemical  Research- 
es, is  as  i  to  2,389. 


AND   NITROUS    ACIDS.  211 

eau  effect  but  a  very  small  portion  of  the  atmosphere,  and 
though  it  were  occasionally  to  produce  a  little  nitric  acid,  yet 
this  never  could  happen  to  such  an  extent  as  to  be  perceivable. 

Emily.  But  how  could  the  nitric  acid  be  known,  and  used, 
before  the  method  of  combining  its  constituents  was  discovered  ? 

^V/r«.  B.  Before  that  period  the  nitric  acid  was  obtained,  and 
it  is  indeed  still  extracted,  for  the  common  purposes  of  art,  from 
tke  compound  salt  which  it  forms  with  potash,  commonly  call- 
ed nitre. 

Caroline.  Why  is  it  so  called  ?  Pray,  Mrs.  B.,  let  these  old 
unmeaning  names  be  entirely  given  up,  by  us  at  least;  and  let 
us  call  this  salt  nitrat  of  potash. 

Mrs.  B.  With  all  my  heart ;  but  it  is  necessary  that  I  should, 
at  least,  mention  the  old  names,  and  more  especially  those 
which  are  yet  in  common  use ;  otherwise,  when  you  meet  with 
them,  you  would  not  be  able  to  understand  their  meaning. 

Emily.  And  how  is  the  acid  obtained  from  this  salt  ? 

Mrs.  B.  By  the  intervention  of  sulphuric  acid,  which  com- 
bines with  the  potash,  and  sets  the  nitric  acid  at  liberty.  This 
I  can  easily  show  you,  by  mixing  some  nitrat  of  potash  and  sul- 
phuric acid  in  this  retort,  and  heating  it  over  a  lamp ;  the  nitric 
acid  will  come  over  in  the  form  of  vapour,  which  we  shall  col- 
lect in  a  glass  bell.  This  acid,  diluted  in  water,  is  commonly 
called  aquafortiSj  if  Caroline  will  allow  me  to  mention  that 
name. 

Caroline.  I  have  often  heard  that  aqua  fortis  will  dissolve  al- 
most all  metals  ;  it  is  no  doubt  because  it  yields  its  oxygen  so 
easily. 

Mrs*  B.  Yes ;  and  from  this  powerful  solvent  property,  it 
derived  the  name  of  aqua  fortis,  or  strong  water.  Do  you  not 
recollect  that  we  oxydated,  and  afterwards  dissolved,  some  cop- 
per in  this  acid  ? 

Emily.  If  I  remember  right,  the  nitrat  of  copper  was  the  first 
instance  you  gave  us  of  a  compound  salt. 

Caroline.  Can  the  nitric  acid  be  completely  decomposed  and 
converted  into  nitrogen  and  oxygen  ? 

Emily.  That  cannot  be  the  case,  Caroline ;  since  the  acid 
can  be  decomposed  only  by  the  combination  of  its  constituents 
ivith  other  bodies. 

.  Wrs.  B.  True  ;  but  caloric  is  sufficient  for  this  purpose.  By 
making  the  acid  pass  through  a  red  hot  porcelain  tube,  it  is  de- 
composed ;  the  nitrogen  and  oxygen  regain  the  caloric  which 
they  had  lost  in  combining,  and  are  thus  both  restored  to  their 
gaseoHS  state, 


212  -OS1   THE    NITRIC 

The  nitric  acid  may  also  be  partly  decomposed,  and  is  by 
this  means  converted  into.  NITROUS  ACID. 

Caroline.  This  conversion  must  be  easily  effected,  as  the  ox- 
ygen is  so  slightly  combined  with  the  nitrogen, 

Mrs.  B.  The  partial  decomposition  of  nitric  acid  is  readily 
effected  by  most  metals;  but  it  is  sufficient  to  expose  the  nitric 
acid  to  a  very  strong  light  to  make  it  give  out  oxygen  gas,  ^.nd 
thus  be  converted  into  nitrous  acid.  Of  this  acid  there  are  va- 
rious degrees,  according  to  the  proportions  of  oxygen  which  it 
contains ;  the  strongest,  and  that  into  which  the  nitric  is  first 
converted.,  is  of  a  yellow  colour,  as  you  see  in  this  bottle. 

Caroline.  How  it 'fumes  when  the  stopper  is  taken  out ! 

Mrs.  B.  The  acid  exists  naturally  in  a  gaseous  state,  and  is 
here  so  strongly  concentrated  in  water,  that  it  is  constantly  es- 
caping. 

Here  is  another  bottle  of  nitrous  acid,  which,  you  see,  is  of  an 
orange  red  ;  this  acid  is  weaker,  the  nitrogen  being  combined 
with  a  smaller  quantity  of  oxygen  ;  and  with  a  still  less  propor- 
tion of  oxygen  it  is  an  olive-green  colour,  as  it  appears  in  this 
third  bottle.  In  short,  the  weaker  the  acid,  the  deeper  is  its 
colour. 

Nitrous  acid  acts  still  more  powerfully  on  some  inflammable 
substances  than  the  nitric. 

Emily.  \  am  surprised  at  that,  as  it  contains  less  oxygen. 

Mr*.  B.  But,  on  the  other  hand,  it  parts  with  its  oxygen 
much  more  readily  :  you  may  recollect  that  we  once  inflamed 
oil  with  this  acid. 

The  next  combinations  of  nitrogen  and  oxygen  form  only 
oxyds  of  nitrogen,  the  first  of  which  is  commonly  called  nitrous 
air  ;  or  more  properly  nitric  oxydgas.*  This  may  be  obtain- 
ed from  nitric  acid,  by  exposing  the  latter  to  the  action  of  met- 
als, as  in  dissolving  them  it  does  not  yield  the  whole  of  its  oxy- 
gen, but  retains  a  portion  of  this  principle  sufficient  to  convert 
it  into  this  peculiar  gas,  a  specimen  of  which  I  have  prepared, 
and  preserved  within  this  inverted  glass  bell. 

Emily.  It  is  a  perfectly  invisible  elastic  fluid. 

Mrs.  B.  Yes;  and  it  may  be  kept  any  length  of  time  in  this 
manner  over  water,  as  it  is  not,  like  the  nitric  and  nitrous  acids, 
absorbable  by  it.  It  is  rather  heavier  than  atmospherical  air, 
and  is  incapable  of  supporting  either  combustion  or  respiration, 

*  To  procure  nitrous  air  put.  into  a  retort  some  filings,  or  shavings  of 
copper,  on  which  pour  nitric  acid,  diluted  with  four  or  five  parts  of 
water ;  then  apply  the  heat  of  a  lamp,  and  receive  the  gas  ia  the  usu- 
al way,  over  water,  C, 


AND   NITROUS    AClDb.  2lo 

t  am  going  to  incline  the  glass  gently  on  one  side,  so  as  to  let 
some  of  the  gas  escape — 

Emily.  How  very  curious ! — --It  produces  orange  fumes  like 
the  nitrous  acid !  that  is  the  more  extraordinary,  as  the  gas 
within  the  glass  is  perfectly  invisible. 

Mrs.  B.  It  would  give  me  much  pleasure  if  you  could  make 
out  the  reason  of  this  curious  change  without  requiring  any  fur- 
ther explanation. 

Caroline.  It  seems, by  the  colour  and  smell,  as  if  it  were  con- 
verted into  nitrous  acid  gas ;  yet  that  cannot  be,  unless  it  com- 
bines with  more  oxygen  ;  and  how  can  it  obtain  oxygen  the 
very  instant  it  escapes  from  the  glass  ? 

Emily.  From  the  atmosphere,  no  doubt.  Is  it  not  so,  Mrs* 
B.r 

Mrs.  B.  You  have  guessed  it  5  as  soon  as  it  comes  in  contact 
with  the  atmosphere,  it  absorbs  from  it  the  additional  quantity 
of  oxygen  necessary  to  convert  it  into  nitrous  acid  gas.  And, 
if  I  now  remove  the  bottle  entirely  from  the  water,  so  as  to 
bring  at  once  the  whole  of  the  gas  into  contact  with  the  atmos- 
phere, this  conversion  will  appear  still  more  striking — 

Emily.  Look,  Caroline,  the  whole  capacity  of  the  bottle  is 
instantly  tinged  of  an  orange  colour  ! 

Mrs.  B.  Thus,  you  see,  it  is  the  most  easy  process  imagina- 
ble to  convert  nitrous  oxyd  gas  into  nitrous  acid  gas.  The 
property  of  attracting  oxygen  from  the  atmosphere,  without 
any  elevation  of  temperature,  has  occasioned  this  gaseous  oxyd 
being  used  as  a  test  for  ascertaining  the  degree  of  purity  of  the 
atmosphere.  I  am  going  to  show  you  how  it  is  applied  to  this 
purpose. — You  see  this  graduated  glass  tube,  which  is  closed  at 
one  end,  (PLATE  X.  fig.  2.) — 1  first  fill  it  with  water,  and  then 
introduce  a  certain  measure  of  nitrous  gas,  which,  not  being  ab- 
sorbable  by  water,  passes  through  it,  and  occupies  the  upper 
part  of  the  tube.  I  must  now  add  rather  above  two-thirds  of 
oxygen  gas,  which  will  just  be  sufficient  to  convert  the  nitrous 
oxyd  gas  into  nitrous  acid  gas. 

Caroline.  So  it  has ! — I  saw  it  turn  of  an  orange  colour  ;  but 
it  immediately  afterwards  disappeared  entirely,  and  the  water, 
you  see,  has  risen,  and  almost  filled  the  tube. 

Mrs.  B.  That  is  because  the  acid  gas  is  absorbable  by  wa- 
ter, and  in  proportion  as  the  gas  impregnates  the  water,  the  lat- 
ter rises  in  the  tube.  When  the  oxygen  gas  is  very  pure,  and 
the  required  proportion  of  nitrous  oxyd  gas  very  exact,  the 
whole  is  absorbed  by  the  water;  but  if  any  other  gas  be  mixed 
with  the  oxygen,  instead  of  combining  with  the  nitrous  oxygen, 
it  will  remain  and  occupy  the  upper  part  of  the  tube  5  or  if  thr 


214  OP   THE   NITRIC 

gases  be  not  in  the  due  proportion,  there  will  be  a  residue  o* 
that  which  predominates. — Before  we  leave  this  subject,  I  must 
not  forget  to  remark  that  nitrous  acid  may  be  formed  by  dissol- 
ving nitrous  oxyd  gas  in  nitric  acid.  This  solution  may  be  ef- 
fected simply  by  making  bubbles  of  nitrous  oxyd  gas  pass 
through  nitric  acid. 

Emily.  That  is  to  say,  that  nitrogen  at  its  highest  degree  of 
oxygenation,  being  mixed  with  nitrogen  at  its  lowest  degree  of 
oxygenation,  will  produce  a  kind  of  intermediate  substance, 
which  is  nitrous  acid. 

'/rs.  S3.  You  have  stated  the  fact  with  great  precision. — 
There  are  various  other  methods  of  preparing  nitrous  oxyd,  and 
of  obtaining  it  from  compound  bodies;  but  it  is  not  necessary 
to  enter  into  these  particulars.  It  remains  for  me  only  to  men- 
tion another  curious  modification  of  oxygenated  nitrogen,  whHi 
has  been  distinguished  by  the  name  of  gaseous  oxyd  of  nitro- 
gen. It  is  but  lately  that  this  sjas  has  been  m  finitely  examin- 
ed, and  its  properties  have  been  investigated  «  ''•'••  iiy  by  Sir  H. 
Davy.  It  has  obtained  also  the  narii^  of  ."M^  aas, 

from  the  very  singular  property  which  that  :  >  v  n  lias  ijs- 
covered  in  it,  of  elevating  the  animal  spirits,  w  :.aled  into 

the  lungs,  to  a  degree  sometimes  resembling  delirium  or  into  AH 
cation. 

Caroline.  Is  it  respirable,  then  ? 

Mrs.  B.  It  can  scarcely  be  called  respirtMp,  RS  it  would  not 
support  life  for  any  length  of  time;  but  it  m..'\  be  hrf-u^ •<!  for 
a  few  moments  without  any  other  effects,  than  th^smjuhr  ex- 
hilaration of  spirits  I  have  just  mentioned.  It  rjff^is  dlff-rent 
people,  however,  in  a  very  different  manner.  Some  be.\,  -re 
violent,  even  outrageous;  others  experience  a  languor,  atten-.led 
with  faintness ;  but  most  a^ree  in  opinion,  th.it  the  sensations  it 
excites  are  extremely  pleasant. 

Caroline.  I  think  I  should  like  to  try  it — how  do  you  breathe 
it? 

Mrs.  B.  By  collecting  the  gas  in  a  bladder,  to  which  a  short 
tube  with  a  stop-cock  is  adapted;  this  is  applied  to  the  month 
with  one  hand,  whilst  the  nostrils  are  kept  closed  \vith  tbeotijt-r, 
that  the  common  air  may  have  no  access.  You  then  altermire- 
ly  inspire,  and  expire  the  gas,  till  you  perceive  its  effects.  I'iit 
I  cannot  consent  to  your  making  the  experiment;  for  i!>e 
nerves  are  sometimes  unpleasantly  affected  by  it,  and  I  wn  'id 
not  run  any  risk  of  that  kind. 

Emily.  I  should  like,  at  least,  to  see  somebody  breathe  it  5 
but  pray  by  what  means  is  this  curious  gas  obtained  ? 


AND    NITROUS    ACID!),  215 

Mrs.  H«  It  is  procured  from  nitrut  of  ammonia,*  an  artifi- 
cial salt  which  yields  this  gas  on  the  application  of  a  gentle 
heat.  I  have  put  some  of  the  salt  into  a  retort,  and  by  the  aid 
of  a  lamp  the  gas  will  be  extricated. 

Caroline.  Bubbles  of  air  begin  to  escape  through  the  neck 
of  the  retort  into  the  water  apparatus ;  will  you  not  collect 
them  ? 

Mrs.  B.  The  gas  that  first  comes  over  need  not  be  preser- 
ved, as  it  consists  of  little  more  than  the  common  air  that  was 
in  th*>  retort ;  besides,  there  is  always  in  this  experiment  a 
quantity  of  watery  vapour  which  must  come  'away  before  the 
nitrous  oxyd  appears. 

Emily.  Watery  vapour  !  Whence  does  that  proceed  ?  There 
is  no  water  in  nitrat  of  ammonia? 

Mrs.  B.  You  must  recollect  that  there  is  in  every  salt  a  quan- 
tity of  water  of  crystallisation,  which  may  be  evaporated  by 
heat  alone.  But,  besides  this,  ^water  is  actually  generated  in 
this  experiment,  as  you  will  see  presently.  First  tell  me,  what 
are  the  constituent  parts  of  nitrat  of  ammonia  ? 

Emily.  Ammonia,  and  nitric  acid  ;  this  salt,  therefore,  con- 
tains three  different  elements,  nitrogen  and  hydrogen,  which 
produce  the  ammonia;  and  oxygen,  which,  with  nitrogen, 
forms  the  acid. 

Mrs.  B.  Well  then,  in  this  process  the  ammonia  is  decom- 

*  To  make  nitrate  of  ammonia,  take  some  nitric  acid,  or  aquafor- 
tis— dilute  it  with  four,  or  five  parts  of  water  ;  put  it  into  a  shallow 
earthen  dish,  and  throw  in  pieces  of  carbonate  of  ammonia,  until  the 
effervescence  ceases.  Evaporate  about  one  third  of  the  liquor  by  a 
gentle  heat,  and  set  it  away  to  crystallize.  The  crystals  are  long  stri- 
ated prisms.  To  procure  the  nitrous  oxide,  or  exhilarating  gas,  and 
to  try  its  effects  by  respiration,  the  following  simple  apparatus  may  be 
used,  where  a  better  is  not  at  hand.  Put  some  nitrate  of  ammonia 
into  an  oil  flask,  having  first  fitted  to  it  a  cork,  and  glass  tube,  bent 
so  as  to  go  under  the  receiver  in  the  water  bath.  Then  apply  the  gen- 
tle heat  of  a  lamp. 

For  a  receiver,  fill  a  large  jug  with  water,  and  invert  it  in  the  water 
bath  :  have  fitted  to  the  jug  a  cork,  having  two  holes  made 
through  it  with  a  burning  iron  ;  into  one  of  these  holes  put  a  glass  tube 
open  at  both  ends,  and  nearly  long  enough  to  reach  the  bottom  of  the 
jug.  Provide  a  large  bladder  furnished  with  a  short  tube  tied  to  it. 
When  the  jug  is  nearly  filled  with  the  gas,  remove,  and  set  it  upright 
by  passing  the  hand  under  its  mouth — then  put  in  the  cork  and  tube, 
the  other  opening  in  the  cork  being  closed.  When  you  wish  to  breathe 
the  gas,  take  the  stopper  out  of  the  cork,  and  pass  in  the  tube  attach- 
ed to  the  bladder.  Then  by  means  of  a  small  tunnel,  pour  water  into 
the  jug  through  the  long  tube,  until!  itdrivs  out  gas  enough  to  fill  the 
bladder.  Mrs.  B.  describes  the  manner  of  oreathing  it. 

Caution.  Let  the  gas  stand  an  hour  or  two  over  water  before  it  is 
breathed.  C.  . 


OF   THE    NITRATS. 

posed ;  the  hydrogen  quits  the  nitrogen  to  combine  with  soni' 
of  the  oxygen  of  the  nitric  acid,  and  forms  with  it  the  waters 
vapour  which  is  now  coming  over.  When  that  is  effected. 
what  will  you  expect  to  find  ? 

Emily.  Nitrous  acid  instead  of  nitric  acid,  and  nitrogen  in- 
stead of  ammonia. 

Mrs.  B.  Exactly  so ;  and  the  nitrous  acid  and  nitrogen  com- 
bine, and  form  the  gaseous  oxyd  of  nitrogen,  in  which  the  pro- 
portion of  oxygen  is  37  parts  to  63  of  nitrogen. 

You  may  have  observed,  that  for  a  little  while  no  bubbles  oi 
air  have  come  over,  and  we  have  perceived  only  a  stream  of 
vapour  condensing  as  it  issued  into  the  water. — Now  bubbles 
of  air  again  make  their  appearance,  and  I  imagine  that  by  this 
time  all  the  watery  vapour  is  come  away,  and  that  we  may  be- 
gin to  collect  the  gas.  We  may  try  whether  it  is  pure,  by  fill- 
ing a  phial  with  it,  and  plunging  a  taper  into  it — yes,  it  will  do 
now,  for  the  taper  burns  brighter  than  in  the  common  air,  and 
with  a  greenish  flame. 

Caroline.  But  how  is  that  ?  I  thought  no  gas  would  support 
combustion  but  oxygen  or  chlorine. 

Mrs.  B.  Or  any  gas  that  contains  oxygen,  and  is  ready  to 
yield  it,  which  is  the  case  with  this  in  a  considerable  degree: 
it  is  not,  therefore,  surprising  that  it  should  accelerate  the  com- 
bustion of  the  taper. 

You  see  that  the  gas  is  now  produced  in  great  abundance: 
we  shall  collect  a  large  quantity  of  it,  and  I  dare  say  that  we 
shall  find  some  of  the  family  who  will  be  curious  to  make  the 
experiment  of  respiring  it.  Whilst  this  process  is  going  on, 
we  may  take  a  general  survey  of  the  most  important  combina- 
tions of  the  nitric  and  nitrous  acids  with  the  alkalies. 

The  first  of  these  is  nitrat  of  potash  commonly  called  nitre 
or  saltpetre. 

Caroline.  Is  not  that  the  salt  with  which  gunpowder  is  made  r 

Mrs  B.  Yes.  Gunpowder  is  a  mixture  of  five  parts  of  ni- 
tre to  one  of  sulphur,  and  one  of  charcoal. — Nitre?  from  its 
great  proportion  of  oxygen,  and  from  the  facility  with  which 
it  yields  it,  is  the  basis  of  most  detonating  compositions. 

Emily.  But  what  is  the  cause  of  the  violent  detonation  of 
gunpowder  when  set  fire  to  ? 

Mrs.  B.  Detonation  may  proceed  from  two  causes ;  the  sud- 
den formation  or  destruction  of  an  elastic  fluid.  In  the  first 
case,  when  either  a  solid  or  liquid  is  instantaneously  converted 
into  an  elastic  fluid,  the  prodigious  and  sudden  expansion  of  the 
body  strikes  the  air  with  great  violence,  and  this  concussion 
produces  the  sound  called  detonation. 


OF    THE    N I  Tit  AT  8.  l 

Caroline.  That  I  comprehend  very  well ;  but  how  can  a 
similar  effect  be  produced  by  the  destruction  of  a  gas  ? 

•Mrs.-  B.  A  gas  can  be  destroyed  only  by  condensing  it  to  u 
liquid  or  solid  state  ;  when  this  takes  place  suddenly,  the  gas, 
in  assuming  a  new  and  more  con  pact  form,  produces  a  vacuum, 
into  which  the  surrounding  air  rush-s  with  great  impetuosity; 
and  it  is  by  that  rapid  and  violent  motion  that  the  sound  is  pro- 
duced. In  all  detonations,  therefore,  gases  are  either  suddenly 
formed,  or  destroyed.  In  that  of  gunpowder,  can  you  tell  me 
which  of  these  two  circumstances  takes  place? 

Emily.  As  gunpowder  is  a  solid,  it  must,  of  course,  produce 
the  gases  in  its  detonation  ;  but  how,  I  cannot  tell. 

Mrs*  B.  The  constituents  of  gunpowder,  when  heated  to  a 
certain  degree,  enter  into  a  number  of  new  combinations,  and 
are  instantaneously  converted  into  a  variety  of  gases,  the  sud- 
den expansion  of  which  gives  rise  to  the  detonation. 

Caroline.  And  in  what  instance  does  the  destruction  or  con- 
densation of  gases  produce  detonation  ? 

Mrs.  B.  I  can  give  you  one  with  which  you  are  well  ac- 
quainted 5  the  sudden  combination  of  the  oxygen  and  hydrogen 
gases. 

'Caroline.  True ;  I  recollect  perfectly  that  hydrogen  de- 
tonates with  oxygen  when  the  two  gases  are  converted  into 
water. 

Mrs.  B.  But  let  us  return  to  the  nitrat  of  potash. — This  salt 
is  decomposed  when  exposed  to  heat,  and  mixed  with  any  com- 
bustible body,  such  as  caibon,  sulphur,  or  metals,  these  substan- 
ces oxydating  rapidly  at  the  expense  of  the  nitrat.  I  must  show 
you  an  instance  of  this. — I  expose  to  the  fire  some  of  the  salt  in 
a  small  iron  ladle,  and,  when  it  is  sufficiently  heated,  add  to  it 
some  powdered  charcoal ;  this  will  attract  the  oxygen  from  the 
salt,  and  be  converted  into  carbonic  acid. — 

Emily.  But  what  occasions  that  crackling  noise,  and  those 
vivid  flashes  that  accompany  it  ? 

Mrs.  B.  The  rapidity  with  which  the  carbonic  acid  gas  is 
formed  occasions  a  succession  of  small  detonations,  which,  to« 
gether  with  the  emission  of  flame,  is  called  deflagration. 

Nitrat  of  ammonia  we  have  already  noticed,  on  account  of 
the  gaseous  oxyd  of  nitrogen  which  is  obtained  from  it. 

Nitrat  of  silver  is  the  lunar  caustic,  so  remarkable  for  its 
property  of  destroying  animal  fibre,  for  which  purpose  it  is  of- 
ten used  by  surgeons. — We  have  said  so  much  on  a  former  oc- 
casion, on  the  mode  in  which  caustics  act  on  animal  matter, 
ihat  I  shall  not  detain  you  any  longer  on  this  subject, 
20 


218  CARBONIC    ACID. 

We  now  come  to  the  CARBONIC  ACID,  which  we  have  airea* 
dy  had  many  opportunities  of  noticing.  You  recollect  that  this 
acid  may  be  formed  by  the  combustion  of  carbon,  whether  in 
its  imperfect  state  of  charcoal,  or  in  its  purest  form  of  diamond. 
And  it  is  not  necessary,  for  this  purpose,  to  burn  the  carbon  in 
oxygen  gas,  as  we  did  in  the  preceding  lecture  ;  for  you  need 
only  light  a  piece  of  charcoal  and  suspend  it  under  a  receiver 
on  the  water  bath.  The  charcoal  will  soon  be  extinguished, 
and  the  air  in  the  receiver  will  be  found  mixed  with  carbonic 
acid.  The  process,  however,  is  much  more  expeditious  if  the 
combustion  be  performed  in  pure  oxygen  gas. 

Caroline.  But  how  can  you  separate  the  carbonic  acid,  ob- 
tained in  this  manner,  from  the  air  with  which  it  is  mixed  ? 

Mrs.  ft.  The  readiest  mode  is  to  introduce  under  the  receiver 
a  quantity  of  caustic  lime,  or  caustic  alkali,  which  soon  attracts 
the  whole  of  the  carbonic  acid  to  form  a  carbonat. — The  alkali 
is  found  increased  in  weight,  and  the  volume  of  the  air  is  dimin- 
ished by  a  quantity  equal  to  that  of  the  carbonic  acid  which  was 
mixed  with  it. 

Emily.  Pray  is  there  no  method  of  obtaining  pure  carbon 
from  carbonic  acid  ? 

Mrs.  B.  For  a  long  time  it  was  supposed  that  carbonic  acid 
was  not  decompoundable;  but  Mr.  Tennant  discovered,  a  few 
years  ago,  that  this  acid  may  be  decomposed  by  burning  phos- 
phorus in  a  closed  vessel  with  carbonat  of  soda  or  carbonat  of 
lime:  the  phosphorus  absorbs  the  oxygen  from  the  carbonat, 
whilst  the  carbon  is  separated  in  the  form  of  a  black  powder. 
This  decomposition,  however,  is  not  effected  simply  by  the  at- 
traction of  the  phosphorus  for  oxygen,  since  it  is  weaker  than 
that  of  charcoal ;  but  the  attraction  of  the  alkali  or  lime  for  the 
phosphoric  acid,  unites  its  power  at  the  same  time. 

Caroline.  Cannot  we  aiake  that  experiment  ? 

Mrs.  /->.  Not  easily ;  it  requires  being  performed  with  ex- 
treme nicety,  in  order  to  obtain  any  sensible  quantity  of  carbon, 
and  the  experiment  is  much  too  delicate  for  me  to  attempt  it. 
But  there  can  be  no  doubt  of  the  accuracy  of  Mr.  Tenmint's  re- 
sults ;  and  all  chemists  now  agree,  that  one  hundred  parts  of 
carbonic  acid  gas  consists  of  about  twenty-eight  parts  of  carbon, 
to  seventy-two  of  oxygen  gas.  But  if  you  recollect,  we  decom- 
posed carbonic  acid  gas  the  other  day  by  burning  potassium 
in  it. 

Caroline.  True,  so  we  did ;  and  found  the  carbon  precipita- 
ted on  the  regenerated  potash. 

Mrs.  B.  Carbonic  acid  gas  is  found  very  abundantly  in  tia- 
ture 5  it  is  supposed  to  form  about  one  thousandth  part  of  the 


CARBONIC    ACID.  21 

atmosphere,  and  is  constantly  produced  by  the  respiration  of 
animals ;  it  exists  in  a  great  variety  of  combinations,  and  is  ex- 
haled from  many  natural  decompositions.  It  is  contained  in  a 
state  of  great  purity  in  certain  caves,  such  as  the  Grotto  del 
Cane,  near  Naples. 

Emily.  I  recollect  having  read  an  account  of  that  grotto,  and 
of  the  cruel  experiments  made  on  the  poor  dogs,  to  gratify  the 
curiosity  of  strangers.  But  1  understood  that  the  vapour  exha- 
led by  this  cave  was  called  Jixed  air. 

Mrs.  B.  That  is  the  name  by  which  carbonic  acid  was  known 
before  its  chemical  composition  was  discovered. — This  gas  is 
more  destructive  of  life  than  any  other ;  and  if  the  poor  animals 
that  are  submitted  to  its  effects  are  not  plunged  into  cold  water 
as  soon  as  they  become  senseless,  they  do  not  recover.  It  ex- 
tinguishes flame  instantaneously.  I  have  collected  some  in  this 
glass,  which  I  will  pour  over  the  candle.* 

Caroline.  This  is  extremely  singular — it  seems  to  extinguish 
the  light  as  it  were  by  enchantment,  as  the  gas  is  invisible.  I 
never  should  have  imagined  that  gas  could  have  been  poured 
like  a  liquid. 

Mrs.  tt.  It  can  be  done  with  carbonic  acid  only,  as  no  other 
:^as  is  sufficiently  heavy  to  be  susceptible  of  being  poured  out  in 
she  atmospherical  air  without  mixing  with  it. 

Emily.  Pray  by  what  means  did  you  obtain  this  gas  ? 

Mrs.  B  I  procured  it  from  marble.  Carbonic  acid  gas  has 
so  strong  an  attraction  for  all  the  alkalies  and  alkaline  earths, 
that  these  are  always  found  in  nature  in  the  state  of  carbonats. 
Combined  with  lime,  this  acid  forms  chalk,  which  may  '>e  con- 
sidered as  the  basis  of  all  kinds  of  marbles,  and  calcareous 
stones.  From  these  substances  carbonic  acid  is  easily  separa- 
ted, as  it  adheres  so  slightly  to  its  combinations,  that  the  carbo- 
nats are  all  decomposable  by  any  of  the  other  acids.  I  can  easi- 
iy  show  you  how  I  obtained  this  gas ;  I  poured  some  diluted 
sulphuric  acid  over  pulverised  marble  in  this  bottle  (the  same 
which  we  used  the  other  day  to  prepare  hydrogen  gas,)  and  the 
gas  escaped  through  the  tube  connected  with  it ;  the  operation 
still  continues,  as  you  may  perceive — 

Emily.  Yes,  it  does;  there  is  a  great  fermentation  in  the  glass 
vessel.  What  singular  commotion  is  excited  by  the  sulphuric 
acid  taking  possession  of  the  lime,  and  driving  out  the  carbonic 
acid ! 

*  Merely  pouring  it  over  a  candle,  will  not  extinguish  it.  Put  ft 
short  piece  of  candl  -,  or  taper,  into  the  bottom  of  a  deep  tumbler,  arid 
then  pour  in  the  gas  and  the  flame  goes  out  as  quick!/  as  though  you 
poured  in  water.  C. 


*»0  GARBOJSIC    AC11>. 

Caroline.  But  did  the  carbonic  acid  exist  in  a  gaseous  stait 
in  the  marble  ? 

Mrs.  B.  Certainly  not ;  the  acid,  when  in  a  state  of  combi- 
nation, is  capable  of  existing  in  a  solid  form. 

Caroline.  Whence,  then,  does  it  obtain  the  caloric  necessary 
to  convert  it  into  gas  ? 

,'Vfrs.  B.  It  may  be  supplied  in  this  case  from  the  mixture  of 
sulphuric  acid  and  water,  which  produces  and  evolution  of  heat, 
even  greater  than  is  required  for  the  purpose;  since,  as  you 
may  perceive  by  touching  the  glass  vessel,  a  considerable  quan- 
tity of  the  caloric  disengaged  becomes  sensible.  But  a  supply 
of  caloric  may  be  obtained  also  from  a  diminution  of  capacity 
for  heat,  occasioned  by  the  new  combination  which  takes 
place;  and,  indeed,  this  must  be  the  case  when  other  acids  are 
employed  for  th«  disengagement  of  carbonic  acid  gas,  which 
do  not,  like  the  sulphuric,  produce  heat  on  being  mixed  with 
water.  Carbonic  acid  may  likewise  be  disengaged  from  its 
combinations  by  heat  alone,  which  restores  it  to  its  gaseous 
state. 

Caroline.  It  appears  to  me  very  extraordinary  that  the  same 
gas,  which  is  produced  by  the  burning  of  wood  and  coals  should 
exist  also  in  such  bodies  as  marble,  and  chalk,  which  are  in- 
combustible substances. 

Jtor*.  B.  I  will  not  answer  that  objection,  Caroline,  because 
I  think  I  can  put  you  in  a  way  of  doing  it  yourself.  Is  carbo- 
nic acid  combustible  ? 

Caroline.  Why,  no — because  it  is  a  body  which  has  been  al- 
ready burnt  ;*  it  is  carbon  only,  and  not  the  acid,  that  is  com- 
bustible. 

Mrs.  B.  Well,  and  what  inference  do  you  draw  from  this  ? 

Caroline.  That  carbonic  acid  cannot  render  the  bodies  with 
which  it  is  united  combustible  ;  but  that  simple  carbon  does, 
and  that  it  is  in  this  elementary  state  that  it  exists  in  wood, 
coals,  and  a  great  variety  of  other  combustible  bodies. — Indeed, 
Mrs.  B.,  you  are  very  ungenerous;  you  are  not  satisfied  with 
convincing  me  that  my  objections  are  frivolous,  but  you  ob'ige 
me  to  prove  them  so  myself. 

Mrs.  B.  You  must  confess,  however,  that  I  make  ample 
amends  for  the  detection  of  error,  when  I  enable  you  to  dis- 
cover the  truth.  You  understand,  now,  I  hope,  that  carbonic 
acid  is  equally  produced  by  the  decomposition  of  chalk,  or  by 

*  Not  burnt  in  the  common  acceptation  of  the  word.  The  carbon 
is  already  united  to  oxygen:  and  therefore  has  no  affinity  for  it.  IP 
the  artificial  production  of  carbonic  acid,  the  carbon  is  burnt  f. 


CA&BONIC    ACID.  221 

f.he  combustion  of  charcoal.  These  processes  are  certainly  of 
a  very  different  nature;  in  the  first  case  the  acid  is  already  for- 
med, and  requires  nothing  more  than  heat  to  restore  it  to  its  gas- 
eous state ,  whilst,  in  the  latter,  the  acid  is  actually  made  by 
the  process  of  combustion. 

Caroline.  I  understand  it  now  perfectly.  But  I  have  just 
been  thinking  of  another  difficulty,  which,  I  hope,  you  will  ex- 
cuse my  not  being  able  to  remove  myself.  How  does  the  irn» 
mense  quantity  of  calcareous  earth,  which  is  spread  all  over  the 
globe,  obtain  the  carbonic  acid  with  which  it  is  combined  ? 

Mrs.  B.  The  question  is,  indeed,  not  very  easy  to  answer; 
but  I  conceive  that  the  general  carbonisation  of  calcareous 
matter  may  have  been  the  effect  of  a  general  combustion,*  oc- 
casioned by  some  revolution  of  our  globe,  and  producing  an 
immense  supply  of  carbonic  acid,  with  which  the  calcareous 
matter  became  impregnated';  or  that  this  may  have  been  effect- 
ed by  a  gradual  absorption  of  carbonic  acid  from  the  atmos- 
phere — But  this  would  lead  us  to  discussions  which  we  cannot 
indulge  in,  without  deviating  too  much  from  our  subject. 

Emily.  How  does  it  happen  that  we  do  not  perceive  the  per- 
nicious effects  of  the  carbonic  acid  which  is  floating  in  the  at- 
mosphere ? 

,'V/rs.  B.  Because  of  the  state  of  very  great  dilution  in  which 
it  exists  there.  Hut  can  you  tell  me,  family,  what  are  the  sour- 
ces which  keep  the  atmosphere  constantly  supplied  with  this 
acid  ? 

Emily.  I  suppose  the  combustion  of  wood,  coals,  and  other, 
substances,  that  contain  carbon. 

J\lrs.  B.  And  also  the  breath  of  animals. 

Caroline.  The  breath  of  animals !  I  thought  you  said  that 
diis  gas  was  not  at  all  respirable,  but  on  the  contrary,  extreme- 
ly poisonous. 

rfirs.  ti.  So  it  is ;  but  although  animals  cannot  breathe  in 
carbonic  acid  gas,  yet,  in  the  process  of  respiration,  they  have 
the  power  of  forming  this  gas  in  their  lungs;  so  that  the  air 
which  we  expire^  or  reject  from  the  lungs,  always  contains  a 
certain  proportion  of  carbonic  acid,  which  is  much  greater  than 
that  which  is  commonly  found  in  the  atmosphere. 

Caroline.  But  what  is  it  that  renders  carbonic  acid  such  a 
deadly  poison  ? 

*  This  idea  is  at  random.  We  cannot  account  for  the  origin  of  car- 
bonic acid  in  its  native,  state  any  better  than  we  can  for  oxygen.  It 
catm-.t  '>e  the  product  of  combustion,  since  it  existed  before  the  growth 
«f  combustible  materials.  C, 

20* 


CARBONIC   ACll?- 

Mrs.  B.  The  manner  in  which  this  gas  destroys  life,  seem* 
to  be  merely  by  preventing  the  access  of  respirable  air ;  tor 
carbonic  acid  gas,  unless  very  much  diluted  with  common  air- 
does  not  penetrate  into  the  lungs,  as  the  windpipe  actually  con- 
tracts and  refuses  it  admittance. — But  we  must  dismiss  this  sub- 
ject at  present,  as  we  shall  have  an  opportunity  of  treating  of 
respiration  much  more  fully,  when  we  come  to  the  chemical 
functions  of  animals. 

Emily.  Is  carbonic  acid  as  destructive  to  the  life  of  vegeta- 
bles as  it  is  to  that  of  animals  ? 

Airs.  B.  If  a  vegetable  be  completely  immersed  in  it,  I  be- 
lieve it  generally  proves  fatal  to  it ;  but  mixed  in  certain  pro- 
portions with  atmospherical  air,  it  is,  on  the  contrary,  very  fa- 
vourable to  vegetation. 

You  remember,  I  suppose,  our  mentioning  the  mineral  wa- 
ters, both  natural  and  artificial,  which  contain  carbonic  acid 
gas? 

Caroline.  You  mean  the  Seltzer  water  ? 

Mrs.  B.  That  is  one  of  those  which  are  the  most  used ; 
there  are,  however,  a  variety  of  others  into  which  carbonic  acid 
enters  as  an  ingredient :  all  these  waters  are  usually  distinguish- 
ed by  the  name  of  acidulous  or  gaseous  mineral  waters. 

The  class  of  salts  called  carbonats  is  the  most  numerous  in 
nature ;  we  must  pass  over  them  in  a  very  cursory  manner,  as 
the  subject  is  far  too  extensive  for  us  to  enter  on  it  in  detail. 
The  state  of  carbonat  is  the  natural  state  of  a  vast  number  of 
minerals,  and  particularly  of  the  alkalies  and  alkaline  earths, 
as  they  have  so  great  an  attraction  for  the  carbonic  acid,  that 
they  are  almost  always  found  comb  necl  with  it;  and  you  may 
recollect  that  it  is  only  by  separating  them  from  this  acid,  that 
they  acquire  that  causticity  and  those  striking  qualities  which  1 
have  formerly  described.  All  marbles,  chalks,  shells,  calca- 
reous spars,  and  lime-stones  of  every  description,  are  neutral 
salts,  in  which  lime,  iheir  common  basis,  has  lost  all  its  charac- 
teristic properties. 

Emily.  But  if  all  these  various  substances  are  formed  by  the 
union  of  lime  with  carbonic  acid,  whence  arises  their  diversity 
of  form  and  appearance  ? 

>\:rs.  B.  Both  from  the  different  proportions  of  their  compo- 
nent parts,  and  from  a  variety  of  foreign  ingredients  which  may 
be  occasionally  blended  with  them  :  the  veins  and  colours  of 
marbles,  for  instance,  proceed  from  a  mixture  of  metallic  sub- 
stances ;  silex  and  alumine  also  frequently  enter  into  these  com- 
binations. The  various  carbonats,  therefore,  which  J  have 


BORACIC   ACID, 

enumerated,  cannot  be  considered  as  pure  unadultered  neutral 
salts,  although  they  certainly  belong  to  that  class  of  bodies. 


CONVERSATION  XIX. 

ON  THE  BORACIC,  FLUORIC,  MURIATIC,  AND  OXYGEN- 
ATED MURIATIC  ACIDS;  AND  ON  MU11IA  TS  —  ON  IO- 
DINE AND  IODIC  ACID. 

Mrs.  B.  WE  now  come  to  the  three  remaining  acids  with 
simple  bases,  the  compound  nature  of  which,  though  long  sus- 
pected, has  been  but  recently  proved.  The  chief  of  these  is 
the  muriatic;  but  I  shall  first  describe  the  two  others,  as  their 
bases  have  been  obtained  more  distinctly  than  that  of  the  muri- 
atic acid. 

You  may  recollect  I  mentioned  the  BORACIC  ACID.  This  is 
found  very  sparingly  in  some  parts  of  Europe,  but  for  the  use 
of  manufactures  we  have  always  received  it  from  the  remote 
country  of  Thibet,  where  it  is  found  in  some  lakes,  combined 
with  soda.  It  is  easily  separated  from  the  soda  by  sulphuric 
acid,  and  appears  in  the  form  of  shining  scales,  as  you  see 
here. 

Caroline.  I  am  glad  to  meet  with  an  acid  which  we  need 
not  be  afraid  to  touch;  for  I  perceive,  from  your  keeping  it  in 
a  piece  of  paper,  that  it  is  more  innocent  than  our  late  acquaint- 
ance, the  sulphuric  and  nitric  acids. 

Airs,  /n  Certainly;  but  being  more  inert,  you  will  not  find 
its  properties  so  interesting.  However  its  decomposition,  and 
the  brilliant  spectacle  it  affurds  when  its  basis  again  unites  with 
oxygen,  atones  for  its  want  of  other  striking  qualities. 

Sir  H.  Davy  succeeded  in  decomposing  the  boracic  acid, 
(which  had  till  then,  been  considered  as  undecornpoimdable,) 
by  various  methods.  On  exposing  this  acid  to  the  Voltaic  bat- 
tery, the  positive  wire  gave  out  oxygen,  and  on  the  negative 
wire  was  deposited  a  black  substance,  in  appearance  resemb- 
ling charcoal.  This  was  the  basis  of  the  acid,  which  Sir  H. 
Davy  has  called  Boracium,  or  Boron. 

The  same  substance  was  obtained  in  more  considerable 
quantities,  by  exposing  the  acid  to  a  great  heat  in  an  iron  gun- 
barrel. 

A  third  method  of  decomposing  the  boracic  acid  consisted  in 
burning  potassium  in  contact  with  it  in  vacuo.  The  potassium 
attracts  the  oxygen  from  the  acid,  and  leaves  its  basis  in  a  sep- 
arate state. 


\ 

524  FLUORIC   ACID. 

The  F^cora position  of  this  acid  I  shall  show  you,  by  burning 
some  of  its  basis,  which  you  see  here,  in  a  retort  full  of  oxygen 
gas.  The  heat  of  a  candle  is  all  that  is  required  for  this  com- 
bustion.— 

Emily.  The  light  is  astonishingly  brilliant,  and  what  beauti- 
ful sparks  it  throws  out ! 

Mrs.  B.  The  result  of  this  combustion  is  the  boracic  acid, 
the  nature  of  which,  you  see,  is  proved  both  by  analytic  and 
synthetic  means.  Its  basis  has  not,  it  is  true,  a  metallic  ap- 
pearance; but  it  makes  very  hard  alloys  with  other  metals. 

Emily.  But  pray,  Mrs.  B.,  for  what  purpose  is  the  boracic 
acid  used  in  manufactures? 

Mrs.  B.  Its  principal  use  is  in  conjunction  with  soda,  that  is, 
in  the  state  of  borat  of  soda,  which  in  the  arts  is  commonly 
called  borax.  This  salt  has  a  peculiar  power  of  dissolving 
metallic  oxyds,  and  of  promoting  the  fusion  of  substances  capa- 
ble of  being  melted ;  it  is  accordingly  employed  in  various  me- 
tallic arts;  it  is  used,  for  example,  to  remove  the  oxyd  from  the 
surface  of  metals,  and  is  often  employed  in  the  assaying  of  me- 
tallic ores. 

Let  us  now  proceed  to  the  FLUORIC  ACID.  This  acid  is  ob- 
tained from  a  substance  which  is  found  frequently  in  mines,  and 
particularly  in  those  of  Derbyshire,  called  Jluor,  a  name  which 
it  acquired  -fcom  the  circumstance  of  its  being  used  to  render 
the  ores  of  metals  more  fluid  when  heated. 

Caroline.  Pray  is  not  this  the  Derbyshire  spar  of  which  so 
many  ornaments  are  made? 

Mrs.  R.  The  same;  but  though  it  has  long  been  employed 
for  a  variety  of  purposes,  its  nature  was  unknown  vmt.il  Scheele, 
the  great  Swedish  chemist,  discovered  that  it  consisted  of  lime 
united  with  a  peculiar  acid,  which  obtained  the  name  of  fluo- 
ric acid.  It  is  easily  separated  from  the  lime  by  the  sulphuric 
acid,  and  unless  condensed  in  water,  ascends  in  the  form  of  gas. 
A  very  peculiar  property  of  this  acid  is  its  union  with  siliceous 
earths,  which  I  have  already  mentioned.  If  the  distillation  of 
this  acid  is  performed  in  glass  vessels,  they  are  corroded,  and 
the  siliceous  part  of  the  glass  comes  over,  united  with  the  gas; 
if  water  is  then  admitted,  part  of  the  silex  is  deposited,  as  you 
may  observe  in  this  jar. 

Caroline.  I  see  white  flakes  forming  on  the  surface  of  the 
water  ;  is  that  silex  ? 

Mrs.  B.  Yes  it  is.  This  power  of  corroding  glass  has  been 
used  for  engraving,  or  rather  etching,  upon  it.  The  jrlass  is 
first  covered  with  a  coat  of  wax,  through  which  the  fi:  urvs  to 
be  engraved  are  to  be  scratched  with  a  pin  ;  then  pouring  the 


MURIATIC    ACID. 

fluoric   acid   over  the  wax,  it  corrodes  the  glass  where  the 
scratches  have  been  made. 

Caroline.  I  should  like  to  have  a  bottle  of  this  acid,  to  make 
engravings.* 

Mrs.  B.  But  you  could  not  have  it  in  a  glass  bottle,  for  in 
that  case  the  acid  would  be  saturated  with  silex,  and  incapable 
of  executing  an  engraving  ;  the  same  thing  would  happen  were 
the  acid  kept  in  vessels  of  porcehun  or  earthen-ware  5  this  acid 
must  therefore  be  both  prepared  and  preserved  in  vessels  of 
silver. 

If  it  be  distilled  from  fluor  spar  and  vitriolic  acid,  in  silver 
or  leaden  vessels,  the  receiver  being  kept  very  cold  during  the 
distillation,  it  assumes  the  form  of  a  dense  fluid,  and  in  that 
state  is  the  most  intensely  corrosive  substance  known.  This 
seems  to  be  the  aeid  combined  with  a  little  water.  It  may  be 
called  hydro  fluoric  add;  and  Sir  H.  Davy  has  been  led,  from 
some  late  experiments  on  the  subject,  to  consider  pure  fluoric 
acid  as  a  compound  of  a  certain  unknown  principle,  which  he 
calls  fluorine,  with  hydrogen. 

Sir  H.  Davy  has  also  attempted  to  decompose  the  fluoric  acid 
by  burning  potassium  in  contact  with  it  ;  but  he  has  not  yet 
been  able  by  this  or  any  other  method,  to  obtain  its  basis  in  a 
distinct  separate  state. 

We  shall  conclude  our  account  of  the  acids  with  that  of  the 
MURIATIC  ACID,  which  is  perhaps  the  most  curious  and  inter- 
esting of  all  of  them.  It  is  found  in  nature  combined  with  so- 
da, lime,  and  magnesia.  Muriat  of  soda  is  the  common  sea- 
salt,  and  from  this  substance  the  acid  is  usually  disengaged  by 
means  of  the  sulphuric  acid.  The  natural  state  of  the  muriatic 
acid  is  that  of  an  invisible  permanent  gas,  at  the  common  tem- 
perature of  the  atmosphere  ;  but  it  has  a  remarkably  strong  at- 
traction for  water,  and  assumes  the  form  of  a  whitish  cloud 
whenever  it  meets  any  moisture  to  combine  with.  This  acid  is 
remarkable  for  its  peculiar  and  very  pungent  smell,  and  pos- 

*  A  bottle  of  fluoric  acid  is  not  easily  obtained.  To  make  etchings 
on  glass,  first  cover  the  glass  with  a  thin  coat  of  bees  wax.  This  is 
done  by  warming  it  over  a  lamp,  and  passing  the  wax  over  the  surface. 
Then  make  the  drawing  by  cutting  through  the  wax  quite  down  to  the 
glasa.  To  do  the  etching  in  the  small  way,  take-  a  lead,  or  tin  cup, 
and  on  the  bottom,  place  about  a  table  spoonful  of  pulverised  fluor 
spar,  and  on  this  pour  sulphuric  acid  enough  to  moisten  it — place  the 
glass  on  the  cup  as  a  cover,  with  the  side  to  he  etched  downward- 
then  set  the  cup  in  warm  water,  or  warm  the  bottom  over  a  lamp, 
taking  care  not  to  melt  the  wix.  In  15  or  20  minutes  or  more,  the 
etching  will  be  done.  In  this  way,  drawings  are  easily  and  beautiful 
!  j  made  on  glass ,  C , 


226  MURIATIC   ACID, 

sesses,  in  a  powerful  degree,  most  of  the  acid  properties.  Here 
is  a  bottle  containing  muriatic  acid  in  a  liquid  state. 

Caroline.  And  how  is  it  liquefied  ? 

J\lrs.  B.  By  impregnating  water  with  it ;  its  strong  attractiou 
for  water  makes  it  very  easy  to  obtain  it  in  a  liquid  form.  Now, 
if  I  open  the  phial,  you  may  observe  a  kind  of  vapour  rising 
from  it,  which  is  muriatic  acid  gas,  of  itself  invisible,  but  made 
apparent  by  combining  with  the  moisture  of  the  atmosphere. 

Emily.  Have  you  not  any  of  the  pure  muriatic  acid  gas  ? 

Mrs.  B.  This  jar  is  full  of  that  acid  in  its  gaseous  state — it 
is  inverted  over  mercury  instead  of  water,  because,  being  ab- 
sorbable  by  water,  this  gas  cannot  be  confined  by  it. — I  shall 
now  raise  the  jar  a  little  on  one  side,  and  sufier  some  of  the  gas 
to  escape. — You  see  that  it  immediately  becomes  visible  in  the 
form  of  a  cloud. 

Emily.  It  must  be,  no  doubt,  from  its  uniting  with  the  mois- 
ture of  the  atmosphere,  that  it  is  converted  into  this  dewy  va» 
pour. 

Mrs.  B.  Certainly  ;  and  for  the  same  reason,  that  is  tosay^ 
its  extreme  eagerness  to  unite  with  water,  this  gas  will  cause 
snow  to  melt  as  rapidly  as  an  intense  fire. 

This  acid  proved  much  more  refractory  when  Sir  H.  Davy 
attempted  to  decompose  it,  than  the  other  two  undecompound- 
ed  acids.  It  is  singular  that  potassium  will  burn  in  muriatic 
acid,  and  be  converted  into  potash,  without  decomposing  the 
acid,  and  the  result  of  this  combustion  is  a  muriat  of  potash; 
for  the  potash,  as  soon  as  it  is  regenerated,  combines  with  the 
muriatic  acid. 

Caroline.  But  how  can  the  potash  be  regenerated,  if  the 
muriatic  acid  does  not  oxydate  the  potassium  ? 

Mrs.  B.  The  potassium,  in  this  process,  obtains  oxygen 
from  the  moisture  with  which  the  muriatic  acid  is  always  com- 
bined, and  accordingly  hydrogen,  resulting  from  the  decompo- 
sition of  the  moisture,  is  invariably  evolved. 

Emily.  But  why  not  make  these  experiments  with  dry  mu- 
riatic acid  ? 

Mrs.  B.  Dry  acids  cannot  be  acted  on  by  the  Voltaic  batte- 
ry, because  acids  are  non-conductors  of  electricity,  unless  mois- 
tened. In  the  course  of  a  number  of  experiments  which  Sir 
H.  Davy  made  upon  acids  in  a  state  of  dryness,  he  observed 
that  the  presence  of  water  appeared  always  necessary  to  devel- 
ope  the  acid  properties,  so  that  acids  are  not  even  capable  of 
reddening  vegetable  blues  if  they  have  been  carefully  deprived 
of  moisture.  This  remarkable  circumstance  led  him  to  suspect, 
that  water,  instead  of  oxygen,  may  be  the  acidifying  principle ; 


OXY-MURIATIC    ACID.  227 

but  this  he  threw  out  rather  as  a  conjecture  than  as  an  establish- 
ed point. 

Sir  H.  Davy  obtained  very  curious  results  from  burning  po- 
tassium in  a  mixture  of  phosphorus  and  muriatic  acid,  and  also 
of  sulphur  and  muriatic  acid  ;  the  latter  detonates  with  great 
violence.  All  his  experiments,  however,  failed  in  presenting 
to  *is  view  the  basis  of  the  muriatic  acid,  of  which  he  was  in 
search  ;  and  he  was  at  last  induced  to  form  an  opinion  respect- 
ing the  nature  of  this  acid,  which  I  shall  presently  explain. 

Emily.  Is  this  acid  susceptible  of  different  degrees  of  oxy- 
genation  ? 

Mrs.  B.  Yes,  for  though  we  cannot  deoxygenate  this  acid, 
yet  v/e  may  add  oxygen  to  it. 

Caroline.  Why  then,  is  not  the  least  degree  of  oxygenation 
of  the  acid  called  the  muriatous,  and  the  higher  degree  the 
muriatic  acid  ? 

Mrs.  B.  Because,  instead  of  becoming,  like  other  acids,  more 
dense,  and  more  acid  by  an  addition  of  oxygen,  it  is  rendered 
on  the  contrary  more  volatile,  more  pungent,  but  less  acid,  and 
less  absorbable  by  water.  These  circumstances,  therefore, 
seem  to  indicate  the  propriety  of  making  an  exception  to  the 
nomenclature.  The  highest  degree  of  oxygenation  of  this  acid 
has  been  distinguished  by  the  additional  epithet  of  oxygenated, 
or,  for  the  sake  of  brevity,  oxy,  so  that  it  is  called  the  oxyge- 
nated, or  oxy  muriatic  acid.  This  likewise  exists  in  a  gaseous 
form,  at  the  temperature  of  the  atmosphere  ;  it  is  also  suscepti- 
ble of  being  absorbed  by  water,  and  can  be  congealed,  or  solid- 
ified, by  a  certain  degree  of  cold. 

Emily.  And  how  do  you  obtain  the  oxy-muriatic  acid  ? 

«Wr«.  B.  In  various  ways  ;  but  it  may  be  most  conveniently 
obtained  by  distilling  liquid  muriatic  acid  over  oxyd  of  manga- 
nese, which  supplies  the  acid  with  the  additional  oxygen.  One 
part  of  the  acid  being  put  into  a  retort,  with  two  parts  of  the 
oxyd  of  manganese,  and  the  heat  of  a  lamp  applied,  the  gas  is 
soon  disengaged,  and  may  be  received  over  water,  as  it  is  but 
sparingly  absorbed  by  it. — I  have  collected  sooie  in  this  jar — * 

Caroline.  It  is  not  invisible,  like  the  generality  of  gases  5  for 
it  is  of  a  yellowish  colour. 

Mrs.  B.  The  muriatic  acid  extinguishes  flame,  whilst,  on  the 
contrary,  the  oxymuriatic  makes  the  flame  larger,  and  gives  it  a 
dark  red  colour.  Can  you  account  tor  this  difference  in  the 
two  acids  ? 

*  Breathing  only  a  tew  bubbles  of  this  gas  is  attended  with  bad, — 
sometimes  with  d  m^erous  (  o.is.-quaioes.  ;  iic  j-oung  chemist,  there- 
fore had  better  not  undertake  to  make  it.  C. 


228  OXY-MUR1AT1C    ACID. 

Emily.  Yes,  I  think  so  ;  the  muriatic  acid  will  not  suppi) 
the  flame  with  the  oxygen  necessary  for  its  support ;  but  when 
this  acid  is  further  oxygenated,  it  will  part  with  its  additional 
quantity  of  oxygen,  and  in  this  way  support  combustion. 

Mrs.  B.  That  is  exactly  the  case  ;  indeed  the  oxygen  added 
to  the  muriatic  acid  adheres  so  slightly  to  it,  that  it  is  separated 
by  mere  exposure  to  the  sun's  rays.  This  acid  is  decomposed 
also  by  combustible  bodies,  many  of  which  it  burns,  and  actual- 
ly inflames,  without  any  previous  increase  of  temperature. 

Caroline.  That  is  extraordinary,  indeed  !  I  hope  you  mean 
to  indulge  us  with  some  of  these  experiments  ? 

Mrs.  B.  I  have  prepared  several  glass  jars  of  oxy-muriatic 
acid  gas  for  that  purpose.  In  the  first  we  shall  introduce  some 
Dutch  gold  leaf. — Do  you  observe  that  it  takes  fire? 

Emily.  Yes,  indeed  it  does — how  wonderful  it  is!  It  became 
immediately  red  hot,  but  was  soon  smothered  in  a  thick  vapour. 
,  Caroline.  What  a  disagreeable  smell  ! 

Mrs.  LJ.  We  shall  try  the  same  experiment  with  phosphorus 
in  another  jar  of  this  acid. — You  had  better  keep  your  hand- 
kerchief to  your  nose  when  I  open  it — now  let  us  drop  into  \\ 
this  little  piece  of  phosphorus — 

Caroline.  It  burns  really ;  and  almost  as  brilliantly  as  in  ox- 
ygen gas  !  But,  what  is  most  extraordinary,  these  combustions 
take  place  without  the  metal  or  phosphorus  being  previously 
lighted,  or  even  in  the  least  heated. 

Mrs.  B.  All  these  curious  effects  are  owing  to  the  very  great 
facility  with  which  this  acid  yields  oxygen  to  such  bodies  as  are 
strongly  disposed  to  combine  with  it.  It  appears  extraordina- 
ry indeed  to  see  bodies,  and  metals  in  particular,  melted  down 
and  inflamed,  by  a  gas  without  any  increase  of  temperature,  ei- 
ther of  the  gas,  or  of  the  combustible.  The  phenomenon,  how- 
ever, is,  you  see,  well  accounted  for. 

Emily.  Why  did  you  burn  a  piece  of  Dutch  gold  leaf  rather 
than  a  piece  of  any  other  metal  ? 

Mrs.  B.  Because,  in  the  first  place,  it  is  a  composition  of 
metals  (consisting  chiefly  of  copper)  which  burns  readily;  and 
I  use  a  thin  metallic  leaf  in  preference  to  a  lump  of  metal,  be- 
cause it  offers  to  the  action  of  the  gas  but  a  small  quantity  of 
matter  under  a  large  surface.  Filings,  or  shavings,  would  an- 
swer the  purpose  nearly  as  well ;  but  a  lump  of  metal,  hough 
the  surface  would  oxydate  with  great  rapidity,  would  not  take 
fire.  Pure  gold  is  not  inflamed  by  oxy-muriatic  acid  gas,  but 
it  is  rapidly  oxydated,  and  dissolved  by  it ;  indeed,  this  acid  is 
the  only  one  that  will  dissolve  gold. 

Emily.  This,  I  suppose,  is  what  is  commonly  called  aqua 


OXY-MURIATIC    ACID.  229 

regta,  which  you  know  is  the  only  thing  that  will  act  upon 
gold. 

Mrs.  B.  That  is  not  exactly  the  case  either  ;  for  aqua  regia 
is  composed  of  a  mixture  of  muriatic  acid  and  nitric  acid. — But 
in  fact,  the  result  of  this  mixture  is  the  formation  of  oxy-rnuriatic 
acid,  as  the  muriatic  acid  oxygenates  itself  at  the  expense  of  the 
nitric;  this  mixture,  therefore,  though  it  bears  the  name  of  ni- 
tre-muriatic acid,  acts  on  gold  merely  in  virtue  of  the  oxy-muri- 
atic  acid  which  it  contains. 

Sulphur,  volatile  oils,  and  many  other  substances,  will  burn 
in  the  same  manner  in  oxy-muriatic  acid  gas ;  but  I  have  not 
prepared  a  sufficient  quantity  of  it,  to  show  you  the  combustion 
of  all  these  bodies. 

Caroline.  There  are  several  jars  of  the  gas  yet  remaining. 

Mrs.  B.  We  must  reserve  these  for  future  experiments.  The 
oxy-muriatic  acid,  does  not,  like  other  acids,  redden  the  blue 
vegetable  colours  ;  but  it  totally  destroys  all  colour,  and  turns 
vegetables  perfectly  white.  Let  us  collect  some  vegetable  sub- 
stances to  put  into  this  glass,  which  is  full  of  gas. 

Emily.  Here  is  a  sprig  of  myrtle — 

Caroline.  And  here  some  coloured  paper — 

Mrs.  B.  We  shall  also  put  in  this  piece  of  scarlet  riband,  and 
a  rose — 

Emily.  Their  colours  begin  to  fade  immediately  !  But  how 
does  the  gas  produce  this  effect? 

Mrs.  B.  The  oxygen  combines  with  the  colouring  matter  of 
these  substances,  and  destroys  it ;  that  is  to  say,  destroys  the 
property  which  these  colours  had  of  reflecting  only  one  kind  of 
rays,  and  renders  them  capable  of  reflecting  them  all,  which, 
you  know,  will  make  them  appear  white.  Old  prints  may  be 
cleansed  by  this  acid,  for  the  paper  will  be  whitened  without 
injury  to  the  impression,  as  printers  ink  is  made  of  materials 
(oil  and  lamp  black)  which  are  not  acted  upon  by  acids. 

This  property  of  the  oxy-muriatic  acid  has  lately  been  em- 
ployed in  manufactures  in  a  variety  of  bleaching  processes  •  but 
for  these  purposes  the  gas  must  be  dissolved  in  water,  as  the 
acid  is  thus  rendered  much  milder  and  less  powerful  in  its  ef- 
fects; for,  in  a  gaseous  state,  it  would  destroy  the  texture  as 
well  as  the  colour  of  the  substance  submitted  to  its  action. 

Caroline.  Look  at  the  things  which  we  put  into  the  gas  •> 
they  have  now  entirely  lost  their  colour  ! 

Mrs.  B.  The  effect  of  the  acid  is^lmost  completed  ;  and  if 
we  were  to  examine  the  quantity  that  remains,  we  should  line! 
it  to  consist  chiefly  of  muriatic  acid. 

21 


2^0  OXY-MURIATIC    A€I1>. 

The  oxy-muriatic  acid  has  been  used  to  purify  the  air  in  fever 
hospitals  and  prisons,  as  it  burns  and  destroys  putrid  effluvia  of 
every  kind.  The  infection  of  the  small-pox  is  likewise  destroy- 
ed by  this  gas,  and  matter  that  has  been  submitted  to  its  influ- 
ence will  no  longer  generate  that  disorder. 

Caroline.  Indeed,  I  think  the  remedy  must  be  nearly  as  bad 
as  the  disease ;  the  oxy-muriatic  acid  has  such  a  dreadfully  suf- 
focating smell. 

Mrs.  B.  It  js  certainly  extremely  offensive  :  but  by  keeping 
the  mouth  shut,  and  wotting  the  nostrils  with  liquid  tmmotiia, 
in  order  to  neutralise  the  vapour  as  it  reaches  the  nose,  its  prej- 
udicial effects  may  be  in  some  degree  prevented.  At  any  rate, 
however,  this  mode  of  disinfection  can  hardly  be  used  in  places 
that  are  inhabited.  And  as  the  vapour  of  nitric  acid,  which  is 
ssarcely  less  efficacious  for  this  purpose,  is  not  at  all  prejudi- 
cial, it  is  usually  preferred  on  such  occasions. 

Caroline.  You  have  not  told  us  yet  what  is  Sir  H.  Davy's 
new  opinion  respecting  the  nature  of  muriatic  acid,  to  which 
you  alluded  a  few  minutes  ago? 

Mrs.  B.  True;  I  avoided  noticing  it  then,  because  you 
could  not  have  understood  it  without  some  previous  knowledge 
of  the  oxy-muriatic  acid,  which  I  have  but  just  introduced  to 
your  acquaintance. 

Sir  H.  Davy's  idea  is  that  muriatic  acid,  instead  of  being  a 
compound,  consisting  of  an  unknown  basis  and  oxygen,  is  form- 
ed by  the  union  of  oxy-muriatic  gas  with  hydrogen? 

Emily.  Have  you  not  told  us  just  now  that  oxy-muriati\ 
gas  was  itself  a  compound  of  muriatic  acid  and  oxygen  ? 

Mrs.  B.  Yes;  but  according  to  Sir  H.  Davy's  hypothesis, 
ox v muriatic  gas  is  considered  as  a  simple  body,  which  con- 
tains no  oxygen — as  a  substance  of  its  own  kind,  which  has  i> 
great  analogy  to  oxygen  in  most  of  its  properties,  though  in 
others  it  differs  entirely  from  it. — According  to  this  view  of  the 
subject,  the  name  of  oxy-muriatic  acid  can  no  longer  be  prop- 
er, and  therefore  Sir  H.  Davy  has  adopted  that  of  chlorine  >  or 
chlorine  gas,  a  name  which  is  simply  expressive  of  its  greenish 
colour;  and  in  compliance  with  that  philosopher's  throry,  we 
Irave  placed  chlorine  in  our  table  among  the  simple  bodies. 

Caroline.  But  what  was  Sir  H.  Davy's  reason  for  adopting 
an  opinion  so  contrary  to  that  which  had  hitherto  prevailed? 

Mrs.  B.  There  are  many  circumstances  which  are  favoura- 
ble to  the  new  docttine;  but  the  clearest  and  simplest  fact  in 
its  support  is,  that  if  hydrogen  gas  and  oxy-muriatic  gas  be 


OXY-MURIATIC    ACID. 


331 


mixed  together,  t)oth  these  gases  disappear,  and  muriatic  acid 
•nis  is  formed. 

Emily.  That  seems  to  be  a  complete  proof;  is  it  not  consid- 
ered as  perfectly  conclusive  ? 

Mrs.  B.  Not  so  decisive  as  it  appears  at  first  sight ;  because 
it  is  argued  by  those  who  still  incline  to  the  old  doctrine,  that 
muriatic  acid  gas,  however  dry  it  may  be,  always  contains  a 
certain  quantity  of  water,  which  is  supposed  essential  to  its  for- 
mation. So  that,  in  the  experiment  just  mentioned,  this  water 
is  supplied  by  the  union  of  the  hydrogen  gas  with  the  oxygen 
of  the  oxy-muriatic  acid  ;  and  therefore  the  mixture  resolves 
itself  into  the  base  of  muriatic  acid  and  water,  that  is,  muriatic 
acid  gas. 

Caroline.  I  think  the  old  theory  must  be  the  true  one  ;  for 
otherwise  how  could  you  explain  the  formation  of  oxy-muriatic 
gas,  from  a  mixture  of  muriatic  acid  and  oxyd  of  manganese? 

Mrs.  B.  Very  easily ;  you  need  only  suppose  that  in  this 
process  the  muriatic  acid  is  decomposed  ;  its  hydrogen  unites 
with  the  oxygen  of  the  manganese  to  form  water,  and  the  chlo- 
rine  appears  in  its  separate  state. 

Emily.  But  how  can  you  explain  the  various  combustions 
which  take  place  in  oxy-muriatic  gas,  if  you  consider  it  as  con- 
taining no  oxygen  ? 

Mrs.  B.  We  need  only  suppose  that  combustion  is  the  result 
of  intense  chemical  action  ;*  so  that  chlorine,  like  oxygen,  in 
Combining  with  bodies,  forms  compounds  which  have  less  ca- 
pacity for  caloric  than  their  constituent  principles,  and,  there- 
fore, caloric  is  evolved  at  the  moment  of  their  combination. 

Emily.  If,  then,  we  may  explain  every  thing  by  either  the- 
ory, to  which  of  the  two  shall  we  give  the  preference  ? 

Mr&.  B.  It  will,  perhaps,  be  better  to  wait  for  more  positive 
.proofs,  if  such  can  be  obtained,  before  we  decide  positively  up- 
on the  subject.  The  new  doctrine  has  certainly  gained  ground 
very  rapidly,  and  may  be  considered  as  nearly  established ; 
but  several  competent  judges  still  refuse  their  assent  to  it,  and 
until  that  theory  is  very  generally  adopted,  it  may  be  as  well 
for  us  still  occasionally  to  use  the  language  to  which  chemists 
have  long  been  accustomed. — But  let  us  proceed  to  the  exami- 
nation of  salts  formed  by  muriatic  acid. 

*  "  Intense  chemical  action,"  neither  explains  the  process,  nor  in~ 
<!eed  conveys  to  the  mind  any  definite  idea.  The  views  of  Sir  H» 
Davy  on  the  composition  of  chlorine,  ore  combatted  by  many  of  thC" 
:^rst  chemists  in  England,  as  well  as  in  this  country.  The  inquisitive 
reader  may  become  acquainted  with  the  grounds  of  dispute  on  both 
sides  by  referring  to  Cooper's  edition  of  Thomson's  chemistry.  C. 


232  MURIATS. 

Among  the  compound  salts  formed  by  muriatic  acid,  the  an* 
riat  of  sodri,  or  common  salt,  is  the  most  interesting.*  The 
uses  and  properties  of  this  salt  are  too  well  known  to  require 
much  Comment.  Besides  the  pleasant  flavour  it  imparts  to  the 
food,  it  is  very  wholesome,  when  not  used  to  excess,  as  it  assists 
the  process  of  digestion. 

Sea- water  is  the  great  source  from  which  muriat  of  soda  is 
extracted  by  evaporation.  But  it  is  also  found  in  large  solid 
masses  in  the  bowels  of  the  earth,  in  England,  and  in  many  oth- 
er parts  of  the  world. 

Emily.  I  thought  that  salts,  when  solid,  were  always  in  the 
state  of  crystals  ;  but  the  common  taole-salt  is  in  the  form  of 
a  coarse  white  powder. 

Mrs.  H.  Crystallisation  depends,  as  you  may  recollect,  on 
the  slow  and  regular  reunion  of  particles  dissolved  in  a  fluid  ; 
common  sea-salt  is  only  in  a  state  of  imperfect  crystallisation, 
because  the  process  by  which  it  is  prepared  is  not  favourable 
to  the  formation  of  regular  crystals.  But  if  you  dissolve  it,  and 
afterwards  evaporate  the  water  slowly,  you  will  obtain  a  regu- 
lar crystallisation. 

Muriat  of  ammonia  is  another  combination  of  this  acid, 
which  we  have  already  mentioned  as  the  principal  source  from 
which  ammonia  is  derived. 

I  can  at  once  show  you  the  formation  of  this  salt  by  the  im- 
mediate combination  of  muriatic  acid  with  ammonia. — These 
two  glass  jars  contain,  the  one  muriatic  acid  gas,  the  other  am- 
moniacal  gas,  both  of  which  are  perfectly  invisible — now,  if  I 
mix  them  together,  you  see  they  immediately  form  an  opaque 
white  cloud,  like  smoke. — If  a  thermometer  was  placed  in  tha 
jar  in  which  these  gases  are  mixed,  you  would  perceive  that 
some  heat  is  at  the  same  time  produced. 

Emily.  The  effects  of  chemical  combinations,  are,  indeed., 
wonderful  ! — How  extraordinary  it  is  that  two  invisible  bodies 
should  become  visible  by  their  union  ! 

Mrs.  B.  This  strikes  you  with  astonishment,  because  it  is  a. 
phenomena  which  nature  seldom  exhibits  to  our  view  ;  but  the 
most  common  of  her  operations  are  as  wonderful,  and  it  is  their 
frequency  only  that  prevents  our  regarding  them  with  equal  ad- 
miration. What  would  be  more  surprising,  for  instance,  than 
combustion,  were  it  not  rendered  so  familiar  by  custom  ? 

*  According  to  Sir  H-  Davy's  views  of  the  nature  of  the  muriatic 
and  oxy-muriatic  acids,  dry  muriat  of  soda  is  a  compound  of  sodium 
and  chlorine,  for  it  may  be  formed  by  the  direct  combination  of  oxy- 
muriatic  gas  and  sodium.  In  his  opinion,  therefore,  what  we  common- 
ly call  muriat  of  soda  contains  neither  soda  nor  muriatic  acid- 


OXY-MUKIA.TS.  -ffSB 

.  That  is  true.— But  pray,  Mrs.  B.,  is  this  white  cloud 
tiie  salt  that  produces  ammonia?  How  different  it  is  from  the 
solid  muriut  of  ammonia  which  you  once  showed  us! 

Mrs.  B.  It  is  the  same  substance  which  first  appears  in  the 
state  of  vapour,  but  will  soon  befeondensed  by  cooling  against 
the  sides  of  the  jar,  in  the  form  of  very  minute  crystals. 

\Ve  may  now  proceed  to  the  oxy-muriats.  In  this  class  of 
salts  the  oxy-muriat  of  potash*  is  the  most  worthy  of  our  atten- 
tion, for  its  striking  properties.  The  acid,  in  this  state  of  com- 
bination, contains  a  still  greater  proportion  of  oxygen  mar? 
when  alone. 

Caroline.  But  how  can  the  oxy-muriatic  acid  acquire  an  in- 
crease of  oxygen  by  combining  with  potash? 

Mrs.  B.  It  does  not  really  acquire  an  additional  quantity  of 
oxygen,  but  it  loses  some  of  the  muriatic  acid,  which  produces 
the  same  effect,  as  the  acid  which  remains  is  proportionably  su- 
per-oxygenated .t 

If  this  salt  be  mixed,  and  merely  rubbed  together  with  sul- 
phur, phosphorus,  charcoal,  or  indeed  any  other  combustibles 
it  explodes  strongly. 

Caroline.  Like  gun-powder,  I  suppose,  it  is  suddenly  con- 
verted into  elastic  fluids? 

Mrs.  B.  Yes;  but  with  this  remarkable  difference,  that  no 
increase  of  temperature,  any  further  than  is  produced  by  gentle 
friction,  is  required  in  Ithis  instance.  Can  you  tell  me  what 
gases  are  generated  by  the  detonation  of  this  salt  with  charcoal  r 

Emily.  Let  me  consider The  oxy-muriatic  acid  parts 

with  its  excess  of  oxygen  to  the  charcoal,  by  which  means  it  is 
converted  into  muriatic  acid  gas;  whilst  the  charcoal,  being 
burnt  by  the  oxygen,  is  changed  to  carbonic  acid  gas — What 
becomes  of  the  potash  I  cannot  tell. 

Mrs.  B.  That  is  a  fixed  product  which  remains  in  the  ves- 
sel. 

Caroline.  But  since  the  potash  does  not  enter  into  the  new 
combinations,  I  do  not  understand  of  what  use  it  is  in  this  ope- 
ration. Would  not  the  oxy- muriatic  acid  and  the  charcoal  pro- 
duce the  same  effect  without  it  ? 

Mrs.  B.  No ;  because  there  would  not  be  that  very  great 
concentration  of  oxygen  which  the  combination  with  the  pot* 
ash  produces,  as  I  have  just  explained. 

*  Oxy-muriat  of  potash  is  prepared  by  passing  chlorine  through  aso- 
lution  of  potash  in  water.  Fhe  process  is  long  and  diiTieult.  C%. 

t  According  to  Sir  H.  Davy's  r^v  views,  just  explained,  oxy-muri- 
at  of  potash  is  a  compound  of  chlorine  with  oxjrd  of  potassium. 

21* 


234  OX 

I  mean  to  show  you  this  experiment,  but  I  would  advise  you 
not  to  repeat  it  alone ;  for  if  care  be  not  taken  to  mix  only  ve- 
ry small  quantities  at  a  time,  the  detonation  will  be  extremely 
violent,  and  may  be  attended  with  dangerous  effects.  You  see 
I  mix  an  exceedingly  small  quantity  of  the  salt  with  a  little 
powdered  charcoal,  in  this  Wedgwood  mortar,  and  rub  them 
together  with  the  pestle — 

Caroline.  Heavens !  How  can  such  a  loud  explosion  be  pro- 
duced by  so  small  a  quantity  of  matter  ? 

'  Jurs.  B.  You  must  consider  that  an  extremely  small  quanti- 
ty of  solid  substance  may  produce  a  very  great  volume  of  gases  5 
and  it  is  the  sudden  evolution  of  these  which  occasions  the 
sound. 

Emily.  Would  not  oxy-muriat  of  potash  make  a  stronger 
gun-powder  than  nitrat  of  potash? 

Mrs.  B.  Yes ;  but  the  preparation,  as  well  as  the  use  of  this 
salt,  is  attended  with  so  much  danger,  that  it  is  never  employed 
for  that  purpose. 

Caroline.  There  is  no  cause  to  regret  it,  I  think ;  for  the 
sommon  gun-powder  is  quite  sufficiently  destructive. 

Mrs.  B.  I  can  show  you  a  very  curious  experiment  with  this 
salt ;  but  it  must  again  be  on  condition  that  you  will  never  at- 
tempt to  repeat  it  by  yourselves.  I  throw  a  small  piece  of 
phosphorus  into  this  glass  of  water;  then  a  little  oxy-muriat  of 
potash;  and,  lastly,  I  pour  in  (by  means  of  this  funnel,  so  as 
to  bring  it  in  contact  with  the  two  other  ingredients  at  the  bot- 
tom of  the  glass)  a  small  quantity  of  jgulphuric  acid — 

Caroline.  This  is,  indeed,  a  beautiful  experiment  !  The 
phosphorus  takes  fire  and  burns  from  the  bottom  of  the  water. 

Emily.  How  wonderful  it  is  to  see  flame  bursting  out  under 
water,  and  rising  through  it  !  Pray,  how  is  this  accounted 
for? 

Mrs.  B.  Cannot  you  find  it  out,  Caroline  ? 

Emily.  Stop — I  think  I  can  explain  it.  Is  it  not  because 
the  sulphuric  acid  decomposes  the  salt  by  combining  with  the 
potash,  so  as  to  liberate  the  oxymuriatic  acid  gas  by  which  the 
phosphorus  is  set  on  fire  ? 

Mrs.  B.,  Very  well,  Emily  ;  andavith  a  little  more  reflection 
you  would  have  discovered  another  concurring  circumstance,, 
which  is,  that  an  increase  of  temperature  is  produced  by  the 
mixture  of  the  sulphuric  acid  and  water,  which  assists  in  pro- 
moting the  combustion  of  the  phosphorus. 

I  must,  before  we  part,  introduce  to  yo1  r  acquaintance  the 
newly-discovered  substance  IODTNE,  which  you  may  recollect 


OXY-MUHIATS.  235 

we  placed  next  to  oxygen  and  chlorine  in  our  table  of  simple 
bodies. 

Caroline.  Is, this  also  a  body  capable  of  maintaining  com- 
bustion like  oxygen  and  chlorine  ? 

Airs,  B.  It  is  ;  and  although  it  does  not  so  generally  disen- 
gage light  and  heat  from  inflammable  bodies,  as  oxygen  and 
chlorine  do,  yet  it  is  capable  of  combining  with  most  of  them  ; 
and  sometimes,  as  in  the  instance  of  potassium  and  phospho- 
rus, the  combination  is  attended  with  an  actual  appearance  of 
light  and  heat. 

Caroline.  But  what  sort  of  a  substance  is  iodine  :  what  is  its 
form,  and  colmir  ? 

Mrs.  B.  It  is  a  very  singular  body,  in  many  respects.  At 
the  ordinary  temperature  of  the  atmosphere,  it  commonly  ap- 
pears in  the  form  of  blueish  black  crystalline  scales,  such  as  you 
see  in  this  tube. 

Caroline.  They  shine  like  black  lead,  and  some  of  the  scales 
have  the  shape  of  lozenges. 

Mrs.  B.  That  is  actually  the  form  which  the  crystals* of  io- 
dine often  assumes.  But  if  we  heat  them  gently,  by  holding 
the  tube  over  the  flame  of  a  candle,  see  what  a  change  takes 
place  in  them. 

Carc'line.  How  curious  !  They  seem  to  melt,  and  the  tube 
immediately  fills  with  a  beautiful  violet  vapour.  But  look, 
Mrs.  B.,  the  same  scales  are  now  appearing  at  the  other  end  of 
the  tube.  •*  ^ 

Mrs.  B.  This  is  in  fact  a  sublimation  of  iodine,  from  one 
part  of  the  tube  to  another  ;  but  with  this  remarkable  peculiar- 
ity, that,  while  in  the  gaseous  state,  iodine  assumes  that  bright 
violet  colour,  which,  as  you  may  already  perceive,  it  loses  as 
the  tube  cools,  and  the  substance  resumes  its  usual  solid  form. 
— - »lt  is  from  the  violet  colour  of  the  gas  that  iodine  has  ob- 
tained its  name. 

Caroline.  But  how  is  this  curious  substance  obtained  ? 

Mrs.  B.  It  is  found  in  the  ley  of  ashes  of  sea- weeds,  after 
the  soda  has  been  separated  by  crystallisation  ;  and  it  is  disen- 
gaged by  means  of  sulphuric  acid,  which  expels  it  from  the  al- 
kaline ley  in  the  form  of  a  violet  gas,  which  may  be  collected 
and  condensed  in  the  way  you  have  just  seen. — This  interesting 
discovery  was  made  in  the  year  1812,  by  M.  Courtois,  a  man- 
ufacturer of  saltpetre  at  Paris. 

Caroline.  And  pray,  Mrs.  B.,  what  is  the  proof  of  iodine  be- 
ing a  simple  body  ? 

Mrs.  B.  It  is  considered  as  a  simple  body,  both  because  it 
is  not  capable  of  being  resolved  into  other  ingredients  5  and  be- 


236 


COMPOSITION 


cause  it  is  itself  capable  of  combining  with  other  bodies,  in  a 
manner  analogous  to  oxygen  and  chlorine.  The  most  curious 
of  these  combinations  is  that  which  it  forms  with  hydrogen  jjas; 
the  result  of  which  is  a  peculiar  gaseous  acid. 

Caroline.  Just  as  chlorine  *nd  hydrogen  gas  form  muriatic 
acid  ?  In  this  respect  chlorine  and  iodine  seem  to  bear  a  strong 
analogy  to  each  other. 

Mrs.  B.  That  is  indeed  the  case  ;  so  that  if  the  theory  of 
the  constitution  of  either  of  these  two  bodies  be  true,  it  must  be 
true  also  in  regard  to  the  other  ;  if  erroneous  in  the  one,  the 
theory  must  fall  in  both. 

But  it  is  now  time  to  conclude  ;  we  have  exsfmined  such  of 
the  acids  and  salts  as  1  conceived  would  appear  to  you  most 
interesting. — I  shall  not  enter  into  any  particulars  respecting 
the  metallic  acids,  as  they  offer  nothing  sufficiently  striking  for 
our  present  purpose. 


CONVERSATION  XX. 

ON  THE  NATURE  AND  COMPOSITION  OF  VEGETABLE 

Mrs.  B.  WE  have  hitherto  treated  only  of  the  simplest  com- 
binations of  elements,  such  as  alkalies,  earths,  acids,  compound 
salts,  ston<^s,  *&e.  ;  all  of  which  belong  to  the  mineral  kingdom, 
It  is  time  now  to  turn  our  attention  to  a  more  complicated  class 
of  compounds,  that  of  ORGANISED  BODIES,  which  \vill  furnish 
us  with  a  new  source  of  instruction  and  amusement. 

Emily.  By  organised  bodies,  I  suppose,  you  mean  the  veget- 
able and  animal  creation  ?  I  have,  however,  but  a  very  vague 
idea  of  the  word  organisation,  and  I  have  often  wished  to  know 
more  precisely  what  it  means. 

Mrs.  B.  Organised  bodies  are  such  as  are  endowed  by  na- 
ture with  various  parts,  peculiarly  constructed  and  adapted  to 
perform  certain  functions  connected  with  life.  Thus  you  may 
observe,  that  mineral  compounds  are  formed  by  the  simple  ef- 
fect of  mechanical  or  chemical  attraction,  and  may  appear  to 
some  to  be  in  a  great  measure  the  productions  of  chance ; 
whilst  organised  bodies  bear  the  most  striking  and  impressive 
marks  of  design,  and  are  eminently  distinguished  by  that  un- 
known principle,  called  life,  from  which  the  various  organs  dev 
rive  the  power  of  exercising  their  respective  functions. 

Caroline.  But  in  what  manner  does  life  enable  these  organs 
to  perform  their  several  functions  ? 


* 

OF    VEGETABLES.  23? 

Mrs,  B.  That  is  a  mystery,  which,  I  fear,  is  enveloped  in 
such  profound  darkness  that  there  is  very  littje  hope  of  our  ev- 
er being  able  to  unfold  it.  We  must  content  ourselves  with  ex- 
amining the  effects  of  this  principle ;  as  for  the  cause,  we  have 
been  able  only  to  give  it  a  name,  without  attaching  any  other 
meaning  to  it  than  the  vague  and  unsatisfactory  idea  of  an 
unknown  agent. 

Caroline.  And  yet  I  think  I  can  form  a  very  cleat  idea  of 
life. 

Mrs.  B.  Pray  let  me  hear  how  you  would  define  it  ? 

Caroline.  It  is  perhaps  more  easy  to  conceive  than  to  ex- 
press— let  me  consider — Is  not  life  the  power  which  enables 
both  the  animal  and  the  vegetable  creation  to  perform  the  vari- 
ous functions  which  nature  has  assigned  to  them  ? 

Mrs.  B.  I  have  nothing  to  object  to  your  definition ;  but  you 
will  allow  me  to  observe,  that  you  have  only  mentioned  the  ef- 
fects which  the  unknown  cause  produces,  without  giving  us  any 
notion  of  the  cause  itself. 

Emily.  Yes,  Caroline,  you  have  told  us  what  life  does,  but 
you  have  not  told  us  what  it  is. 

Mrs.  B.  We  may  study  its  operations,  but  we  should  puzzle 
ourselves  to  no  purpose  by  attempting  to  form  an  idea  of  its 
real  nature. 

We  shall  begin  with  examining  its  effects  in  the  vegetable 
world,  which  constitutes  the  simplest  class  of  organised  bodies  ; 
these  we  shall  find  distinguished  from  the  mineral  creation,  not 
only  by  their  more  complicated  nature,  but  by  the  power  which 
they  possess  within  themselves,  of  forming  new  chemical  ar- 
rangements of  their  constituent  parts,  by  means  of  appropriate 
organ's.  Thus,  though  all  vegetables  are  ultimately  composed 
of  hydrogen,  carbon,  and  oxygen,  (with  a  few  other  occasional 
ingredients,)  they  separate  and  combine  these  principles  by 
their  various  organs,  in  a  thousand  ways,  and  form,  with  them, 
different  kinds  of  juices  and  solid  parts,  which  exist  ready  made 
in  vegetables,  and  may,  therefore,  be  considered  as  their  imme*- 
diate  materials. 

These  are  : 

Sap,  Resins, 

Mucilage,  Gum  Resins, 

Sugar,  Balsams, 

Fecula,  Caoutchouc, 

Gluten,  Extractive  colouring  Matter, 

Fixed  Oil,  Tannin, 

Volatile  Oil,  Woody  Fibre, 

Camphor,  Vegetable  Acids,  fyc, 


338  COMPOSITION 

Caroline.  What  a  long  list  of  names !  I  did  not  suppose  that 
a  vegetable  was  composed  of  half  so  many  ingredients. 

Mrs.  B.  You  must  not  imagine  that  every  one  of  these  mate- 
rials is  formed  in  each  individual  plant.  I  only  mean  to  say, 
that  they  are  all  derived  exclusively  from  the  vegetable  king- 
dom. 

Emily.  But  does  each  particular  part  of  the  plant,  such  as 
ihe  root,  the  bark,  the  stem,  the  seeds,  the  leaves,  consist  of  one 
or  these  ingredients  only,  or  of  several  of  them  combined  to- 
gether ? 

Airs.  B.  I  believe  there  is  no  part  of  a  plant  which  can  be 
said  to  consist  solely  of  any  one  particular  ingredient ;  a  cer- 
tain number  of  vegetable  materials  must  always  be  combined 
for  the  formation  of  any  particular  part,  (of  a  seed  for  instance,) 
and  these  combinations  are  carried  on  by  sets  of  vessels,  or  mi- 
nute organs,  which  select  from  other  parts,  and  bring  together, 
the  several  principles  required  for  the  developement  and  growth 
of  those  particular  parts  which  they  are  intended  to  form  and  to 
maintain. 

Emily.  And  are  not  these  combinations  always  regulated  by 
the  laws  of  chemical  attraction  ? 

Mrs.  B.  No  doubt ;  the  organs  of  plants  cannot  force  princi- 
ples to  combine  that  have  no  attraction  for  each  other ;  nor 
can  they  compel  superior  attractions  to  yield  to  those  of  inferi- 
or power  ;  they  probably  act  rather  mechanically,  by  bringing 
into  contact  such  principles,  and  in  such  proportions,  as  will, 
by  their  chemical  combination,  form  the  various  vegetable  pro- 
ducts. 

Caroline.  We  may  then  consider  each  of  these  organs  as  a 
curiously  constructed  apparatus,  adapted  for  the  performance  of 
a  variety  of  chemical  processes. 

Mrs.  B.  Exactly  so.  As  long  as  the  plant  lives  and  thrives, 
the  carbon,  hydrogen,  and  oxygen,  (the  chief  constituents  of  its 
immediate  materials,)  are  so  balanced  and  connected  together, 
that  they  are  not  susceptible  of  entering  into  other  combinations ; 
but  no  sooner  does  death  take  place,  than  this  state  of  equilibri- 
um is  destroyed,  and  new  combinations  produced. 

Emily.  But  why  should  death  destroy  it ;  for  these  princi- 
ples must  remain  in  the  same  proportions,  and  consequently,  I 
should  suppose,  in  the  same  order  of  attractions  ? 

Mrs.  B.  You  must  remember,  that  in  the  vegetable,  as  well 
as  in  the  animal  kingdom,  it  is  by  the  principle  of  life  that  the 
organs  are  enabled  to  act ;  when  deprived  of  that  agent  or  sti- 
mulus, their  power  ceases,  and  an  order  of  attractions  succeeds 


OF    VEGKTABLBb. 

similar  to  that  which  would  take  place  in  mineral  or  unorgan- 
ised matter. 

Emily.  It  is  this  new  order  of  attractions,  I  suppose,  that 
destroys  the  organisation  of  the  plant  alter  death  ;  for  if  the 
same  combinations  still  continued  to  prevail,  the  plant  would 
always  remain  in  the  state  in  which  it  died  ? 

Mrs.  B.  Arid  that,  you  know,  is  never' the  case;  plants  may 
be  partially  preserved  for  some  time  after  death,  by  drying  ; 
but  in  the  natural  course  of  events  they  all  return  to  the  state 
of  simple  elements  ;  a  wise  and  admirable  dispensation  of  Pro- 
vidence, by  which  dead  plants  are  rendered  n't  to  enrich  the 
soil,  and  become  subservient  to  the  nourishment  of  living  veget- 
ables. 

Caroline.  But  we  are  talking  of  the  dissolution  of  plants, 
before  we  have  examined  them  in  their  living  state. 

Mrs.  B>  That  is  true,  my  dear.  But  I  wished  to  give  you  a 
general  idea  of  the  nature  of  vegetation,  before  we  entered  into 
particulars.  Besides,  it  is  not  so  irrelevant  as  you  suppose  to 
talk  of  vegetables  in  their  dead  state,  since  we  cannot  analyze 
them  without  destroying  life ;  and  it  is  only  by  hastening  to 
submit  them  to  examination,  immediately  after  they  have  ceas- 
ed to  live,  that  we  can  anticipate  their  natural  decomposition. 
There  are  two  kinds  of  analysis  of  which  vegetables  are  sus- 
ceptible ;  first,  that  which  separates  them  into  their  immediate 
materials,  such  as  sap,  resin,  mucilage.  &c.  ;  secondly,  that 
which  decomposes  them  into  their  primitive  elements,  as  car- 
bon, hydrogen,  and  oxygen. 

Emily.  Is  there  not  a  third  kind  of  analysis  of  plants,  which 
consists  in  separating  their  various  parts,  as  the  stem,  the 
leaves,  and  the  several  organs  of  the  flower  r 

Mrs.  B.  That,  my  dear,  is  rather  the  department  of  the  bo- 
tanist ;  we  shall  consider  these  different  parts  of  plants  only, 
as  the  organs  by  which  the  various  secretions  or  separations  are 
performed  ;  but  we  must  first  examine  the  nature  of  these  se- 
cretions. 

The  sap  is  the  principal  material  of  vegetables,  since  it  con- 
tains the  ingredients  that  nourish  every  part  of  the  plant.  The 
basis  of  this  juice,  which  the  roots  suck  up  from  the  soil,  is  wa- 
ter ;  this  holds  in  solution  the  various  other  ingredients  requir- 
ed by  the  several  parts  of  the  plant,  which  are  gradually  secre- 
ted from  the  sap  by  the  different  organs  appropriated  to  that 
purpose,  as  it  passes  them  in  circulating  through  the  plant. 

.\lucus,  or  mucilage,  is  a  vegetable  substance,  which,  like  all 
the  others,  is  secreted  from  the  sap  ;  when  in  excess,  it  exudes 
from  trees  in  the  form  of  gum. 


240  COMPOSITION 

Caroline.  Is  that  the  gum  so  frequently  used  instead  of  paste 
or  glue  ? 

J^trs  B.  It  is;  almost  all  fruit-trees  yield  some  sort  of  gum, 
but  that  most  commonly  used  in  the  arts  is  obtained  from  a  spe- 
cies of  acacia-tree  in  Arabia,  and  is  called  gum  arable ;  it 
forms  the  chief  nourishment  of  the  natives  of  those  parts,  who 
obtain  it  in  great  quantities  from  incisions  which  they  make  in 
the  trees. 

Caroline.  I  did  not  know  that  gu;n  was  eatable. 

Mrs.  B.  There  is  an  account  of  a  whole  ship's  company  be- 
ing saved  from  starving  by  feeding  on  the  cargo,  which  was 
gum  Senegal.  I  should  not,  however,  imagine,  that  it  would 
be  either  a  pleasant  or  a  particularly  eligible  diet  to  those  who 
have  not,  from  their  birth,  been  accustomed  to  it.  It  is,  how- 
ever, frequently  taken  medicinally,  and  considered  as  very 
nourishing.  Several  kinds  of  vegetable  acids  may  be  obtain- 
ed, by  particular  processes,  from  gum  or  mucilage,  the  princi- 
pal of  which  is  called  the  mucous  acid. 

Sugar  is  not  found  in  its  simple  state  in  plants,  but  is  always 
mixed  with  gum,  sap,  or  other  ingredients;  this  saccharine 
matter  is  to  be  met  with  in  every  vegetable,  but  abounds  most 
in  roots,  fruits,  and  particularly  in  the  sugar-cane. 

Emily.  If  all  vegetables  contain  sugar,  why  is  it  extracted 
exclusively  from  the  sugar-cane  ? 

Mrs.  b.  Because  it  is  both  most  abundant  in  that  plant,  and 
most  easily  obtained  from  it.  Besides,  the  sugars  produced  by 
other  vegetables  differ  a  little  in  their  nature. 

During  the  late  troubles  in  the  West-Indies,  when  Europe 
was  but  imperfectly  supplied  with  sugar,  several  attempts  were 
made  to  extract  it  from  other  vegetables^  and  very  good  sugar 
was  obtained  from  parsnips  and  from  carrots;  but  the  process 
was  too  expensive  to  carry  this  enterprise  to  any  extent. 

Caroline.  I  should  think  that  sugar  might  be  more  easily  ob- 
tained from  sweet  fruits,  such  as  figs,  dates,  &c. 

j\irs.  B.  Probably ;  but  it  would  be  still  more  expensive, 
from  the  high  price  of  those  fruits. 

Emily.  Fray,  in  what  manner  is  sugar  obtained  from  the  su- 
gar-cane ? 

Mrs.  B.  The  juice  of  this  plant  is  first  expressed  by  passing 
it  between  two  cylinders  of  iron.  It  is  then  boiled  with  lime- 
water,  which  makes  a  thick  scum  rise  to  the  surface.  The 
clarified  liquor  is  let  off  below  and  evaporated  to  a  very  small 
quantity,  after  which  it  is  suffered  to  crystallize  by  standing  in 
a  vessel,  the  bottom  of  which  is  perforated  with  holes,  that  are 
imperfectly  stopped,  in  order  that  the  syrup  may  drain  off, 


OP    VEGETABLES.  241 

The  sugar  obtained  by  this  process  is  a  coarse  brown  powder, 
commonly  called  raw  or  moist  sugar;  it  undergoes  another  op- 
eration to  be  refined  and  converted  into  loaf  sugar.  For  this 
purpose  it  is  dissolved  in  water,  and  afterwards  purified  by  an 
animal  fluid  called  albumen.  White  of  eggs  chiefly  consist  of 
this  fluid,  which  is  also  one  of  the  constituent  parts  of  blood  ; 
and  consequently  eggs,  or  bullocks'  blood,  are  commonly  used 
for  this  purpose. 

The  albuminous  fluid  being  diffused  through  the  syrup,  com- 
bines with  all  the  solid  impurities  contained  in  it,  and  rises  with 
them  to  the  surface,  where  it  forms  a  thick  scum  ;  the  clear  li- 
quor is  then  again  evaporated  to  a  proper  consistence,  and 
poured  into  moulds,  in  which,  by  a  confused  crystallisation,  it 
forms  loaf-sugar.  But  an  additional  process  is  required  to  whi- 
ten it;  to  'his  effect  the  mould  is  inverted,  and  its  open  base  is 
covered  with  clay,  through  which  water  is  made  to  pass;  the 
water  slowly  trickling  through  the  sugar,  combines  with  and 
carries  off  the  colouring  matter. 

Caroline.  I  am  very  glad  to  hear  that  the  blood  that  is  used 
to  purify  sugar  does  not  remain  in  it;  it  would  be  a  disgusting 
idea.  I  have  heard  of  some  improvements  by  the  late  Mr. 
Howard,  in  the  process  of  refining  sugar.  Pray  what  are 
they? 

Airs.  B.  It  would  be  much  too  long  to  give  you  an  account 
of  the  process  in  detail.  But  the  principal  improvement  relates 
to  the  mode  of  evaporating  the  syrup,  in  order  to  bring  it  to  the 
consistency  of  sugar.  Instead  of  boiling  the  syrup  in  a  large 
copper,  over  a  strong  fire,  Mr.  Howard  carries  off  the  water  by 
means  of  a  large  air-pump,  in  a  way  similar  to  that  used  in  Mr. 
Leslie's  experiment  for  freezing  water  by  evaporation;  that  is, 
the  syrup  being  exposed  to  a  vacuum,  the  water  evaporates 
quickly,  with  no  greater  heat  than  that  of  a  little  steam,  which 
is  introduced  round  the  boiler.  The  air-pump  is  of  course  of 
large  dimensions,  and  is  worked  by  a  steam  engine.  A  great 
saving  is  thus  obtained,  and  a  striking  instance  afforded  of  the 
power  of  science  in  suggesting  useful  economical  improvements. 

Emily.  And  pray  how  is  sugar-candy  and  barley-sugar  pre- 
pared ? 

Mrs.  B.  Candied  sugar  is  nothing  more  than  the  regular 
crystals,  obtained  by  slow  evaporation  from  a  solution  of  sugar. 
Barley-sugar  is  sugar  melted  by  heat,  and  afterwards  cooled  in 
moulds  of  a  spiral  form. 

Sugar  may  be  decomposed  by  a  red  heat,  and,  like  all  other 
vegetable  substances,  resolved  into  carbonic  acid  and  hydrogen. 
The  formation  and  the  decomposition  of  sugar  afford  many  ve- 

22 


242  COMPOSITION 

ry  interesting  particulars,  which  we  shall  fully  examine,  after 
having  gone  through  the  other  materials  of  vegetables.  We 
sha'l  find  that  there  is  reason  to  suppose  that  sugar  is  not,  like 
the  other  materials,  secreted  from  the  sap  by  appropriate  or- 
gans; but  that  it  is  formed  by  a  peculiar  process  with  which 
you  are  not  yet  acquainted. 

Caroline.  Pray,  is  not  honey  of  the  same  nature  as  sugar  ? 

Mrs.  B.  Honey  is  a  mixture  of  saccharine  matter  and  gum. 

Emily.  I  thought  that  honey  was  in  some  measure  an  ani- 
mal swbstance,  as  it  is  prepared  by  the  bees. 

Mrs.  B.  It  is  rather  collected  by  them  from  flowers,  and  con- 
veyed to  their  store-houses,  the  hives.  It  is  the  wax  only  that 
undergoes  a  real  alteration  in  the  body  of  the  bee,  and  is  thence 
converted  into  an  animal  substance.* 

Manna  is  another  kind  of  sugar,  which  is  united  with  a  nau- 
seous extractive  matter,  to  which  it  owes  its  peculiar  taste  and 
colour.  It  exudes  like  gum  from  various  trees  in  hot  climates, 
some  of  which  have  their  leaves  glazed  by  it. 

The  next  of  the  vegetable  materials  is  fecula  ;  this  is  the 
general  name  given  to  the  farinaceous  substance  contained  in 
all  seeds,  and  in  some  roots,  as  the  potatoe,  parsnip,  &c.  It 
is  intended  by  nature  for  the  first  aliment  of  the  young  vegeta- 
ble; but  that  of  one  particular  grain  is  become  a  favourite  and 
most  common  food  of  a  large  part  of  mankind. 

Emily.  You  allude,  I  suppose,  to  bread,  which  is  made  of 
wheat-flour  ? 

Mrs.  B.  Yes.  The  fecula  of  wheat  contains  also  another 
vegetable  substance  which  seems  peculiar  to  that  seed,  or  at 
least  has  not  as  yet  been  obtained  from  any  other.  This  is 
gluten,  which  is  of  a  sticky,  ropy,  elastic  nature  ;  and  it  is  sup- 
posed to  be  owing  to  the  viscous  qualities  of  this  substance,  that 
wheat-flour  forms  a  much  better  paste  than  any  other. 

Emily.  Gluten,  by  your  description,  must  be  very  likegum  ? 

Mrs.  B.  In  their  sticky  nature  they  certainly  have  some  re- 
semblance ;  but  gluten  is  essentially  different  from  gum  in  oth- 
er points,  and  especially  in  its  being  insoluble  in  water,  whilst 
gum,  you  know,  is  extremely  soluble. 

The  oils  contained  in  vegetables  all  consist  of  hydrogen  and 
carbon  in  various  proportions.  They  are  of  two  kinds,  fixed 
and  vo/afe7e,'both  of  which  we  formerly  mentioned.  Do  you- 

*  It  was  the  opinion  of  Huher,  that  the  bees  prepared  (he  wax  from 
honey  and  sugar,  There  is,  however,  found  on  the  leaves  of  some 
plants  a  substance,  having  all  the  properties  of  wax  ;  and  that  bees- 
wax  itself  is  not  an  animal  substance,  is  clear  from  ite  analysis.  C, 


OP   VEGETABLES.  243 

remember  in  what  the  difference  between  fixed  and  volatile  oil 
consists? 

Emily.  If  I  recollect  rightly,  the  former  are  decomposed  by 
heat,  whilst  the  latter  are  merely  volatilised  by  it. 

Airs.  B.  Very  well.  Fixed  oil  is  contained  only  in  the 
seeds  of  plants,  excepting  in  the  olive,  in  which  it  is  produced 
in,  and  expressed  from,  the  fruit.  We  have  already  observed 
that  seeds  contain  also  fecula;  these  two  substances,  united 
with  a  little  mucilage,  form  the  white  substance  contained  in 
the  seeds  or  kernels  of  plants,  and  is  destined  for  the  nourish- 
ment of  the  young  plant,  to  which  the  seed  gives  birth.  The 
milk  of  almonds,  which  is  expressed  from  the  seed  of  that  name, 
is  composed  of  these  three  substances. 

Emily.  Pray,  of  what  nature  is  the  linseed  oil  which  is  used 
in  painting  ?  ^ 

Mrs.  B.  It  is  a  fixed  on,  obtained  from  the  seed  of  flax. 
Nut  oil,  which  is  frequently  us&l  for  the  same  purpose,  is  ex- 
pressed from  walnuts. 

Olive  oil  is  that  whichjs  best  adapted  to  culinary  purposes. 

Caroline.  And  what  are  the  oils  used  for  burning  ? 

Mrs.  B.  Animal  oils  most  commonly;  but  the  preference 
*iven  to  them  is  owing  to  their  being  less  expensive;  for  vege- 
table oils  burn  equally  well,  and  are  more  pleasant,  as  their 
smell  is  not  offensive. 

Emily.  Since  oil  is  so  good  a  combustible,  what  is  the  rea- 
son that  lamps  so  frequently  require  trimming  ? 

*M?%  B.  This  sometimes  proceeds  from  the  construction  of 
the  lamp,  which  may  not  be  sufficiently  favourable  to  a  per- 
fect combustion  ;  but  there  is  certainly  a  defect  in  the  nature  of 
oil  itself,  which  renders  it  necessary  for  the  best-constructed 
lamps  to  be  occasionally  trimmed.  This  defect  arises  from  a 
portion  of  mucilage  which  it  is  extremely  difficult  to  separate 
from  the  oil,  and  which  being  a  bad  combustible,  gathers  round 
the  wick,  and  thus  impedes  its  combustion,  and  consequently 
dims  the  light. 

Caroline.  But  will  not  oils  burn  without  a  wick  ? 

Mrs.  B.  Not  unless  their  temperature  be  elevated  to  five  or 
six  hundred  degrees  ;  the  wick  answers  this  purpose,  as  I  think 
I  once  before  explained  to  you.  The  oil  rises  between  the  fi- 
bres of  the  cotton  by  capillary  attraction,  and  the  heat  of  the 
burning  wick  volatilises  it,  and  brings  it  successively  to  the  tem- 
perature at  which  it  is  combustible. 

Emily.  I  suppose  the  explanation  which  you  have  given  with 
regard  to  the  necessity  of  trimming  lamps,  applies  also  to  cart" 
dies,  which  so  often  require 


-44  COMPOSITION 

Mrs.  /?.  I  believe  it  does ;  at  least,  in  some  degree.  But 
besides  the  circumstance  just  explained,  the  common  sort  of 
oils  are  not  very  highly  combustible,  so  that  the  heat  produced 
by  a  candle,  which  is  a  coarse  kind  of  animal  oil,  being  insuffi- 
cient to  volatilise  them  completely,  a  quantity  of  soot  is  gradu- 
ally deposited  on  the  wick,  which  dims  the  light,  and  retards 
the  combustion. 

Caroline.  Wax  candles  then  contain  no  incombustible  mat- 
ter, since  they  do  not  require  snuffing  ? 

Mrs.  B.  Wax  is  a  much  better  combustible  than  tallow,  but 
still  not  perfectly  so,  since  it  likewise  contains  some  particles 
that  are  unfit  for  burning;  but  when  these  gather  round  the 
wick,  (which  in  a  wax  light  is  comparatively  small,)  they  weigh 
it  down  on  one  side,  and  fall  off  together  with  the  burnt  part  of 
the  wick. 

Caroline.  As  oils  are  such  gooa  combustibles,  I  wonder  that 
they  should  require  so  great  an  elevation  of  temperature  before 
they  begin  to  burn  ? 

Mrs.  B.  Though  fixed  oils  will  not  enter  into  actual  combus- 
tion below  the  temperature  of  about  four  hundred  degrees,*  yet 
they  will  slowly  absorb  oxygen  at  the  common  temperature  of 
the  atmosphere.  Hence  arises  a  variety  of  changes  in  oils 
which  modify  their  properties  and  uses  in  the  arts. 

If  oil  simply  absorbs,  and  combines  with  oxygen,  it  thickens 
and  changes  to  a  kind  of  wax.  This  change  is  observed  to 
take  place  on  the  external  parts  of  certain  vegetables,  even  du- 
ring their  life.  But  it  happens  in  many  instances  that  the  oil 
does  not  retain  all  the  oxygen  which  it  attracts,  but  that  part  of 
it  combines  with,  or  burns,  the  hydrogen  of  the  oil,  thus  form* 
ing  a  quantity  of  water,  which  gradually  goes  off  by  evapora- 
tion. In  this  case  the  alteration  of  the  oil  consists  not  only  in 
the  addition  of  a  certain  quantity  of  oxygen,  but  in  the  diminu- 
tion of  the  hydrogen.  These  oils  are  distinguished  by  the  name 
of  drying  oils.  Linseed,  poppy,  and  nut-oils,  are  of  this  de- 
scription. 

Emily.  I  am  well  acquainted  with  drying  oils,  as  I  continu- 
ally use  them  in  painting.  But  I  do  not  understand  why  the 
acquisition  of  oxygen  on  one  hand,  and  a  loss  of  hydrogen  on 
the  other,  should  render  them  drying  ? 

Mrs.  B.  This,  I  conceive,  may  arise  from  two  reasons ;  ei- 

*  This  statement  is  too  low.  None  of  the  fixed  oils  boil  at  a  les? 
temperature  than  600  degrees,  nor  will  they  burn  until  converted  into 
vapour;  consequently  they  cannot  burn  at  a  lower  temperature  than 
600.  C. 


OF   VEGfcTABLfiSc  245 


ther  from  the  oxygen  which  is  added  being  less  favourable  to 
the  state  of  fluidity  than  the  hydrogen,  which  is  subtracted  ;  or 
from  this  additional  quantity  of  oxygen  giving  rise  to  new  com- 
binations, in  consequence  of  which  the  most  fluid  parts  of  the. 
oil  are  liberated  and  volatilised. 

For  the  purpose  of  painting,  the  drying  quality  of  oil  is  fur- 
ther increased  by  adding  a  quantity  of  oxyd  of  lead  to  it,  by 
which  means  it  is  more  rapidly  oxygenated. 

The  rancidity  of  oil  is  likewise  owing  to  tlieir  oxygenation, 
In  this  case  a  new  order  of  attraction  takes  place,  from  which  a 
peculiar  acid  is  formed,  called  the  sebacic  acid. 

Caroline.  Since  the  nature  and  composition  of  oil  is  so  well 
known,  pray  could  not  oil  be  actually  made,  by  combining  its 
principles  ? 

Mrs.  B.  That  is  by  no  means  a  necessary  consequence  ;  for 
there  are  innumerable  varieties  of  compound  bodies  which  we 
can  decompose,  although  we  are  unable  to  reunite  their  ingredi- 
ents. This,  however,  is  not  the  case  with  oU,  as  it  has  very 
lately  been  discovered,  that  it  is  possible  to  form  oil,  by  a  pe* 
culiar  process,  from  the  action  of  oxygenated  muriatic  acid  gas 
on  hydro-carbonate.* 

We  now  pass  to  the  volatile  or  essential  oils.  These  form, 
the  basis  of  all  the  vegetable  perfumes,  and  are  contained,  more 
or  less,  in  every  part  of  the  plant  excepting  the  seed  ;  they  are, 
at  least,  never  found  in  that  part  of  the  seed  which  contains  the 
embrio  plant. 

Emily.  The  smell  of  flowers,  then,  proceeds  from  volatile 
oil  ? 

Mrs.  B.  Certainly  ;  but  this  oil  is  often  most  abundant  in  the 
rind  of  fruits,  as  in  oranges,  lemons,  &c.  from  which  it  may  be 
extracted  by  the  slightest  pressure  ;  it  is  found  also  in  the  leaves 
-of  plants,  and  even  iri  the  wood. 

Caroline.  Is  it  not  very  plentiful  in  the  leaves  of  mint,  and 
of  thyme,  and  all  the  sweet-smelling  herbs? 

Mrs.  R.  Yes,  remarkably  so  ;  and  in  geranium  leaves  also, 
which  have  a  much  more  powerful  odour  than  the  flowers. 

The  perfume  of  sandal  fans  is  an  instance  of  its  existence  in 
wood.  In  short,  all  vegetable  oilours  or  perfumes  are  produced 
by  the  evaporation  of  particles  of  these  volatile  oils. 

*  Hydro-carbonate,  ia  also  called  olejlant  or  oil  making  gas,  on  ac- 
count if  the  supposed  property  here  mentioned.  But  later  experi- 
ments have  shown  that  th>^  substance  it  forms  with  chlorine,  is  not  aa 
oil,  out  a  kind  of  ether,  foeuce  it  is  now  known  *||der  the  name  of  cMo- 
fic  ether.  IA 

22* 


246 

Emjfy.  They  are,  I  suppose,  very  light,  and  of  very  thin  con- 
sistence, since  they  are  so  volatile  ? 

Mrs.  B.  They  vary  very  much  in  this  respect,  some  of  them 
being  as-thick  as  butter,  whilst  others  are  as  fluid  as  water.  J« 
order  to  be  prepared  for  perfumes,  or  essences,  tiiese  oils  are 
first  properly  purified,  and  then  either  distilled  with  spirit  of 
Wine,  as  is  the  case  with  lavender  water,  or  simply  mixed  with 
a  large  proportion  of  water,  as  is  often  done  with  regard  to  pep- 
permint. Frequently,  also,  these  odoriferous  waters  are  prepar- 
ed merely  by  soaking  the  plants  in  water,  and  distilling.  The 
water  then  comes  over  impregnated  with  the  volatile  oil. 

Caroline.  Such  waters  are  frequently  used  to  take  spots  of 
grease  out  of  cloth,  or  silk  ;  how  do  they  produce  that  effect  ? 

Mrs.  B.  By  combining  with  the  substance  that  forms  these 
stains;  for  volatile  oils,  and  likewise  the  spirit  in  which  they 
are  distilled,  will  dissolve  wax.  tallow,  spermaceti,  and  resins  ; 
if,  therefore,  the  spot  proceeds  from  any  of  these  substances,  it 
will  remove  it.  Insects  of  every  kind  have  a  great  aversion  to 
perfumes,  so  that  volatile  oils  are  employed  with  success  in  mu- 
seums for  the  preservation  of  stuffed  birds  and  other  species  of 


Caroline.  Pray  does  not  the  powerful  smell  of  camphor  pro- 
>ceed  from  a  volatile  oil  ? 

Mrs.  B.  Camphor  seems  to  be  a  substance  of  its  own  kind, 
remarkable  by  many  peculiarities.  But  if  not  exactly  of  the 
same  nature  as  volatile  oil,  it  is  at  least  very  analogous  to  it.  It 
is  obtained  chiefly  from  the  camphor-tree,  a  species  of  laurel 
which  grows  in  China,  and  in  the  Indian  isles,  from  the  stem 
and  roots  of  which  it  is  extracted.*  Small  quantities  have  also 
been  distilled  from  thyme,  sage,  and  other  aromatic  plants;  and 
it  is  deposited  in  pretty  large  quantities  by  some  volatile  oils  af- 
ter long  standing.  It  is  extremely  volatile  and  inflammable. 
It  is  insoluble  in  water,  but  is  soluble  in  oils,  in  which  state,  as 
well  as  in  its  solid  form,  it  is  frequently  applied  to  medicinal 
purposes.  Amongst  the  particular  properties  of  camphor, 
there  is  one  too  singular  to  be  passed  over  in  silence.  If  you 
take  a  small  piece  of  camphor,  and  place  it  on  the  surface  of  a 
bason  of  pure  water,  it  will  immediately  begin  to  move  round 
and  round  with  great  rapidity  ;  but  if  you  pour  into  the  basin  a 
single  drop  of  any  odoriferous  fluid,  it  will  instantly  put  a  stop 
to  this  motion.  You  can  at  any  time  try  this  very  simple  ex* 

*  Camphor  comesjJiiefly  from  Japan.  It  is  obtained'  by  distilling 
the  wood  of  the  laums  camphara,  or  camphor  tree,  with  water,  iu 
large  iron  pots,  with  earthen  caps  stuffed  with  straw.  The  camphor 
sublimes  and  concretes  upon  the  straw.  C. 


OP    VEGETABLES.  24? 

pei'miem  ;  but  you  must  not  expect  that  I  shall  be  able  to  ac- 
count for  this  phenomenon,  as  nothing  satisfactory  has  yet  been 
idvanced  for  its  explanation. 

Caroline.  It  is  very  singular  indeed;  and  I  will  certainly 
try  the  experiment.  Pray  what  are  resins,  which  you  just  now 
mentioned  ? 

Mrs.  B.  They  are  volatile  oils,  that  have  been  acted  on,  and 
peculiarly  modified,  by  oxygen. 

Caroline.  They  are,  therefore, oxygenated  volatile  oils? 

Mrs.  B.  Not  exactly ;  for  the  process  does  not  appear  to 
consist  so  much  in  the  oxygenation  of  the  oil,  as  in  the  combus- 
tion of  a  portion  of  its  hydrogen,  and  a  small  portion  of  its  car- 
bon. For  when  resins  are  artificially  made  by  the  combination 
of  volatile  oils  with  oxygen,  the  vessel  in  which  the  process  is 
performed  is  bedewed  with  water,  and  the  air  included  within 
is  loaded  with  carbonic  acid. 

Emily.  This  process  must  be,  in  some  respects,  similar  to 
that  for  preparing  drying  oils  ? 

Mrs.  B.  Yes;  and  it  is  by  this  operation  that  both  of  them 
acquire  a  greater  degree  of  consistence.  Pitch,  tar,  and  tur- 
pentine, are  the  most  common  resins;  they  exude  from  the  pine 
and  fir  trees.  Copal,  mastic,  and  frankincense,  are  also  of  this 
class  of  vegetable  substances. 

Emily.  Is  it  of  these  resins  that  the  mastic  and  copal  varnish- 
es, so  much  used  in  painting,  are  made  ? 

Mrs.  B.  Yes.  Dissolved  either  in  oil,  or  in  alcohol,  resins 
form  varnishes.  From  these  solutions  they  may  be  precipita- 
ted by  water,  in  which  they  are  insoluble.  This  I  can  easily 
show  you. — If  you  will  pour  some  water  into  this  glass  of  mas- 
tic varnish,  it  will  combine  with  the  alcohol  in  which  the  resin 
is  dissolved,  and  the  latter  will  be  precipitated  in  the  form  of  a 
white  cloud — 

l-'.mily.  It  is  so.  And  yet  how  is  it  that  pictures  or  draw- 
ings, varnished  with  this  solution,  may  safely  be  washed  with 
water  ? 

Mrs.  13,  As  the  varnish  dries,  the  alcohol  evaporates,  and 
the  dry  varnish  or  resin  whjplPremains,  not  being  soluble  in  wa- 
ter, will  not  be  acted  on  b/it* 

There  is  a  class  of  compound  resins  called  gum  resins, 
which  are  precisely  what  their  name  denotes,  that  is  to  say,  re- 
sins combined  with  mucilage.  Myrrh  and  assafcetida  are  of 
this  description. 

Caroline.  Is  it  possible  that  a  substance  of  so  disagreeable  a 
smell  as  assafcetida  can  be  formed  from  a  volatile  oil  ? 

Mrs.  B.  The  odour  of  volatile  oils  is  by  no  means  always 


248  COMPOSITION 

grateful.  Onions  and  garlic  derive  their  smell  from  volatile 
oils,  as  well  as  roses  and  lavender. 

There  is  still  another  form  under  which  volatile  oils  present 
themselves,  which  is  that  of  balsams.  These  consist  of  resin- 
ous juices  combined  with  a  peculiar  acid,  called  the  benzoic  ac- 
id. Balsams  appear  to  have  been  originally  volatile  oils,*  the 
oxygenation  of  which  has  converted  one  part  into  a  resin,  and 
the  other  part  into  an  acid,  which,  combined  together,  form  a 
balsam  ;  such  are  the  balsams  of  Peru,  Tolu,  &c. 

We  shall  now  take  leave  of  the  oils  and  their  various  modi- 
fications, and  proceed  to  the  next  vegetable  substance,  which  is 
caoutchouc.  This  is  a  white  milky  glutinous  fluid,  which  ac- 
quires consistence,  and  blackens  in  drying,  in  which  state  it 
forms  the  substance  with  which  you  are  so  well  acquainted,  un- 
der the  name  of  gum-elastic. 

Caroline.  I  am  surprised  to  hear  that  gum-elastic  was  ever 
white,  or  ever  fluid  !  And  from  what  vegetable  is  it  procured  ? 

Mrs.  B.  It  is  obtained  from  two  or  three  different  species  of 
trees,  in  the  East-Indies,  and  South-America,  by  making  inci- 
sions in  the  stem.  The  juice  is  collected  as  it  trickles  from 
these  incisions,  and  moulds  of  clay,  in  the  form  of  little  bottles 
of  gum-elastic,  are  dipped  into  it.  A  layer  ,of  this  juice  ad- 
heres to  the  clay  and  dries  on  it :  and  several  layers  are  suc- 
cessively added  by  repeating  this  till  the  bottle  is  of  sufficient 
thickness.  It  is  then  beaten  to  break  down  the  clay,  which  is 
easily  shaken  out.  The  natives  of  the  countries  where  this 
substance  is  produced  sometimes  make  shoes  and  boots  of  it  by 
a  similar  process,  and  they  are  said  to  be  extremely  pleasant 
and  serviceable,  both  from  their  elasticity,  and  their  being  water- 
proof. 

The  substance  which  comes  next  in  our  enumeration  of  the 
immediate  ingredients  of  vegetables,  is  extractive  matter.  This 
is  a  term,  which,  in  a  general  sense,  may  be  applied  to  any  sub- 
stance extracted  from  vegetables;  but  it  is  more  particularly 
understood  to  relate  to  the  extractive  colouring  matter  of  plants. 
A  s^reat  variety  of  colours  are  prepared  from  the  vegetable 
kingdom,  both  for  the  purposes  qfcg:>aiuting  and  of  dying  ;  all 
the  colours  called  lakes  are  of  th^Wescription  ;  but  they  are 
less  durable  than  mineral  colours,  for,  by  long  exposure  to  the 
atmosphere,  they  either  darken  or  turn  yellow. 

Emily.  I  know  that  in  painting,  the  lakes  are  reckoned  far 

*  This  is  an  erroneous  idea.  Balsams  are  original  and  peculiar  sub- 
stances, and  consist  chiefly  of  resinous  matter  in  a  s.-mifluid  state. 
The  benzoic  acid  is  most  probably  formed  during  the  process  by  which 
it  is  obtained.  C 


OlT    VEGETABLES.  24$ 

less  durable  colours  than  the  ochres ;  but  what  is  the  reason  of 
it? 

Airs.  B.  The  change  which  takes  place  in  vegetable  colours 
is  owing  chiefly  to  the  oxygen  of  the  atmosphere  slowly  burn- 
ing their  hydrogen,  and  leaving,  in  some  measure,  the  blackness 
of  the  carbon  exposed.  Such  changes  cannot  take  place  in 
ochre,  which  is  altogether  a  mineral  substance. 

Vegetable  colours  have  a  stronger  affinity  for  animal  than 
for  vegetable  substances,  and  this  is  supposed  to  be  owing  to  a 
small  quantity  of  nitrogen  which  they  contain.  Thus,  silk  and 
worsted  will  take  a  much  finer  vegetable  dye  than  linen  and 
cotton. 

Caroline,  Dying,  then,  is  quite  a  chemical  process  ? 

Mrs.  B.  Undoubtedly.  The  condition  required  to  form  a 
good  dye  is,  that  the  colouring  matter  should  be  precipitated, 
or  fixed,  on  the  substance  to  be  dyed,  and  should  form  a  com- 
pound not  soluble  in  the  liquids  to  which  it  will  probably  be 
exposed.  Thus,  for  instance,  printed  or  dyed  linens  or  cottons 
must  be  able  to  resist  the  action  of  soap  and  water,  to  which 
they  must  necessarily  be  subject  in  washing  ;  and  woollens  and 
silks  should  withstand  the  action  of  grease  and  acids,  to  which 
they  may  accidentally  be  exposed. 

Caroline.  But  if  linen  and  cotton  have  not  a  sufficient  affini» 
ty  for  colouring  matter,  how  are  they  made  to  resist  the  action 
of  washing,  which  they  always  do  when  they  are  well  printed  ? 

Mrs.  B.  When  the  substance  to  be  dyed  has  either  no  affin- 
ity for  the  colouring  matter,  or  not  sufficient  power  to  retain  it, 
the  combination  is  effected,  or  strengthened,  by  the  intervention 
of  a  third  substance,  called  a  mordant,  or  basis.  The  mordant 
must  have  a  strong  affinity  both  for  the  colouring  matter  and  the 
substance  to  be  dyed,  by  which  means  it  causes  them  to  com- 
bine and  adhere  together. 

Caroline.  And  what  are  the  substances"that  perform  the  of- 
fice of  thus  reconciling  the  two  adverse  parties  ? 

Mrs.  B.  The  most  common  mordant  is  sulphat  of  alumine,  or 
alum.  Oxyds  of  tin  and  iron,  in  the  state  of  compound  salts, 
are  likewise  used  for  that  purpose. 

Tannin  is  another  vegetable  ingredient  of  great  importance 
in  the  arts.  It  is  obtained  chiefly  from  the  bark  of  trees  ;  but 
it  is  found  also  in  nut-galls,  and  in  some  other  vegetables. 

Emily.  Is  that  the  substance  commonly  called  tan,  which  is 
used  in  hot  houses  ? 

Mrs.  B.  Tan  is  the  prepared  bark  in  which  the  peculiar  sub- 
stance, tannin,  is  contained..  But  the  use  of  tan  in  hot-houses 


250  COMPOSITION 

is  of  much  less  importance  than  in  the  operation  of  tannmg,by 
which  the  skin  is  converted  into  leather. 

Emily.  Pray,  how  is  this  operation  performed  ? 

Mrs.  B.  Various  methods  are  employed  for  this  purpose., 
which  all  consist  in  exposing  skin  to  the  action  of  tannin,  or  of 
substances  containing  this  principle,  in  sufficient  quantities,  and 
disposed  to  yield  it  to  the  skin.  The  most  usual  way  is  to  in- 
fuse coarsely  powdered  oak  bark  in  water,  and  to  keep  the  skin 
immersed  in  this  infusion  for  a  certain  length  of  time.  During 
this  process,  which  is  slow  and  gradual,  the  skin  is  found  to 
have  increased  in  weight,  and  to  have  acquired  a  considerable 
tenacity  and  impermeability  to  water.  This  effect  may  be 
much  accelerated  by  using  strong  saturations  of  the  tanning 
principle  (which  can  be  extracted  from  bark,)  instead  of  em- 
ploying the  bark  itself.  But  this  quick  mode  of  preparation 
does  not  appear  to  make  equally  good  leather. 

Tannin  is  contained  in  a  great  variety  of  astringent  vegetable 
substances,  as  galls,  the  rose-tree,  and  wine  ;  but  it  is  no  where 
so  plentiful  as  in  bark.  All  these  substances  yield  it  to  water, 
from  which  it  may  be  precipitated  by  a  solution  of  isinglass,  or 
glue,  with  which  it  strongly  unites  arid  forms  an  insoluble  com- 
pound. Hence  its  valuable  property  of  combining  with  skin, 
(which  consists  chiefly  of  glue,)  and  of  enabling  it  to  resist  the 
action  of  the  water. 

Emily.  Might  we  not  see  that  effort  by  pouring  a  little  melt- 
ed isinglass  into  a  glass  of  wine,  which  you  say  contains  tan- 
nin ? 

Mrs.  B.  Yes.  I  have  prepared  a  solution  of  isinglass  for 
that  very  purpose. — Do  you  observe  the  thick  muddy  precipi- 
tate ? — That  is  the  tannin  combined  with  the  isinglass. 

Caroline.  This  precipitate  must  then  be  of  the  same  nature 
as  leather  ? 

Mrs.  B  It  is  composed  of  the  same  ingredients  ;  but  the 
organisation  and  texture  of  the  skin  being  wanting,  it  has  neither 
the  consistence  nor  the  tenacity  of  leather. 

Caroline.  One  mi^ht  suppose  that  men  who  drink  large 
quantities  of  red  wine,  stand  a  chance  of  having  the  coats  of 
their  stomachs  converted  into  leather,  since  tannin  has  so  strong 
an  affinity  for  skin  ? 

Airs.  B.  It  is  not  impossible  but  that  the  coats  of  their  stom- 
achs may  be,  in  some  measure,  tanned,  or  hardened  by  th«;  con- 
stant use  of  this  liquor  ;  but  you  must  remember  that  where  a 
number  of  other  chemical  agents  are  concerned,  and,  above 
all,  where  life  exists,  no  certain  chemical  inference  can  be 
drawn. 


OF    VEGETABLES.  251 

I  must  not  dismiss  this  subject,  without  mentioning  a  recent 
discovery  of  Mr.  Hatchett,  which  relates  to  it.  This  gentle- 
man found  that  a  substance  very  similar  to  tannin,  possessing  all 
its  leading  properties,  and  actually  capable  of  tanning  leather, 
may  be  produced  by  exposing  carbon,  or  any  substance  con- 
taining carbonaceous  matter,  whether  vegetable,  animal,  or  mi- 
neral, to  the  action  of  nitric  acid.* 

Caroline.  And  is  not  this  discovery  very  likely  to  be  of  use 
to  manufactures  ? 

Mrs.  B.  That  is  very  doubtful,  because  tannin,  thus  artifi- 
cially prepared,  must  probably  always  be  more  expensive  than 
that  which  is  obtained  from  bark.  But  the  fact  is  extremely 
curious,  as  it  affords  one  of  those  very  rare  instances  of  chemis- 
try being  able  to  imitate  the  proximate  principles  of  organised 
Bodies. 

The  last  of  the  vegetable  materials  is  woody  fibre  ;  it  is  the 
hardest  part  of  plants.  The  chief  source  from  which  this  sub- 
stance is  derived  is  wood,  but  it  is  also  contained,  more  or  less, 
in  every  solid  part  of  the  plant.  It  forms  a  kind  of  skeleton  of 
the  part  to  which  it  belongs,  and  retains  its  shape  after  all  the 
other  materials  have  disappeared.  It  consists  chiefly  of  car- 
bon, united  with  a  small  proportion  of  salts,  and  the  other  con- 
stituents common  to  all  vegetables. 

Emily.  It  is  of  woody  fibre,  then,  that  the  common  charcoal 
is  made  ? 

Mrs.  B.  Yes.  Charcoal,  as  you  may  recollect,  is  obtained 
from  wood,  by  the  separation  of  all  its  evaporable  parts. 

Before  we  take  leave  of  the  vegetable  materials,  it  will  be 
proper,  at  least,  to  enumerate  the  several  vegetable  acids  which 
we  either  have  had,  or  may  have  occasion  to  mention.  I  be- 
lieve I  formerly  told  you  that  their  basis,  or  radical,  was  uni- 
formly composed  of  hydrogen  and  carbon,  and  that  their  dif- 
ference consisted  only  in  the  various  proportions  of  cfxygen 
which  they  contained. 

The  following  are  the  names  of  the  vegetable  acids  : 
The  mucous  acid,  obtained  from  gum  or  mucilage; 
Suberic        -        -       from  cork ; 

*  To  make  artificial  tannin,  Mr  Hatchett  used  100  grains  of  char- 
coal with  500  of  nitric  acid,  diluted  with  twice  its  weight  of  water, 
This  mixture  was  heated  and  then  suffered  to  digest  for  two  days  ; 
more  acid  was  then  added,  and  the  digestion  continued  untill  the  char- 
coal was  dissolved.  The  solution  being  evaporated  to  dry  ness, 
leaves  a  dark  brown  mass.  This  is  the  tannin  in  question,  Its  taste  is 
bitter  and  highly  astringent.  C, 


252  COMPOSITION 

Camphoric  -         -     from  camphor ; 
Benzoic  -      from  balsams ; 

Gallic  -        from  galls,  bark,  &c. 

Malic  -        from  ripe  fruits , 

Citric  -        from  lemon  juice  5 

Oxalic       -  from  sorrelj 

Succinic  -         -    from  amber  ; 
Tartarous         -     -     from  tartrit  of  potash  ; 
Acetic  -        from  vinegar. 

They  are  all  decomposable  by  heat,  soluble  in  water,  and 
turn  vegetable  blue  colours  red.  The  succinic,  the  tartaroits, 
and  the  acetous  acids,  are  the  products  of  the  decomposition 
of  vegetables,  we  shall,  therefore,  reserve  their  examination  for 
a  future  period. 

The  oxalic  acid,  distilled  from  sorrel,  is  the  highest  term  of 
vegetable  acidification  ;  for,  if  more  oxygen  be  added  to  it,  it 
loses  its  vegetable  nature,  and  is  resolved  into  carbonic  acid  and 
water  ;  therefore,  though  all  the  other  acids  may  be  converted 
into  the  oxalic  by  an  addition  of  oxygen,  the  oxalic  itself  is  not 
susceptible  of  a  further  degree  of  oxygenation  ;  nor  can  it  be 
made,  by  any  chemical  processes,  to  return  to  a  state  of  lower 
acidification.* 

To  conclude  this  subject,  I  have  only  to  add  a  few  words  on 
the  gallic  acid  . . . 

Caroline.  Is  not  this  the  same  acid  before  mentioned,  which 
forms  ink,  by  precipitating  sulphat  of  iron  from  its  solution  ? 

Mrs.  B.  Yes.  Though  it  is  usually  extracted  from  galls,  on 
account  of  its  being  most  abundant  in  that  vegetable  substance, 
it  may  also  be  obtained  from  a  great  variety  of  plants.  It  con- 
stitutes what  is  called  the  astringent  principle  of  vegetables  ; 
it  is  generally  combined  with  tannin,  and  you  will  find  that  an 
infusion  of  tea,  coffee,  bark,  red  wine,  or  any  vegetable  sub- 
stance that  confains  the  astrinuent  principle,  will  make  a  black 
precipitate  with  a  solution  of  sulphat  of  iron. 

Caroline.  But  pray  what  are  galls  ? 

Mrs.  B.  They  are  excrescences  which  grow  on  the  bark  of 

*  Oxalic  acid  may  be  formed  artificially.  Put  one  ounce  of  white 
sugar,  powdered,  into  a  retort,  and  pour  on  three  ounces  of  nitric  acid. 
When  the  solution  is  over,  make  the  liquor  boil,  and  when  it  acquires 
a  reddish-brown  colour,  add  three  ounces  more  of  nitric  acid.  Con- 
tinue the  boiling  untill  the  fumes  cease,  and  the  colour  of  the  liquor 
vanishes.  Then  let  the  liquor  be  poured  into  a  wide  vessel,  and  on 
white,  slender  crystals  will  be  formed,  These  are  oxalic  acid. 

C. 


OF    VEGETABLES,  253 

young  oaks,  ami  are  occasioned  by  an  insect  which  wounds  the 
bark  of  trees,  and  lays  its  eggs  in  the  aperture.  The  lacerated 
vessels  of  the  tree  then  discharge  their  contents,  and  form  an 
excrescence,  which  affords  a  defensive  covering  for  these  eggs. 
The  insect,  when  come  to  life,  first  feeds  on  this  excrescence, 
and  some  time  afterwards  eats  its  way  out,  as  it  appears  from  a 
hole  which  is  formed  in  all  gall-nuts  that  no  longer  contain  an 
insect.  It  is  in  hot  climates  only  Wiat  strongly  astringent  gall- 
nuts  are  found  ;  those  which ,are  used  for  the  purpose  of  ma- 
king ink  are  brought  from  Aleppo. 

Emily.  But  are  not  the  oak-apples,  which  grow  on  the  leaves 
of  the  oak  in  this  country,  of  a  similar  nature  ? 

Mrs.  B.  Yes  ;  only  they  are  an  inferior  species  of  galls, 
containing  less  of  the  astringent  principle,  and  therefore  less 
applicable  to  useful  purposes. 

Caroline.  A  re  the  vegetable  acids  never  found  but  in  their 
pure  uncombined  state? 

Mrs.  B.  By  no  means ;  on  the  contrary,  they  are  frequently 
met  with  in  the  state  of  compound  salts;  these,  however,  are  in 
general  not  fully  saturated  with  the  salifiable  bases,  so  that  the 
acid  predominates;  and,  in  this  state,  they  are  called  acidulous 
salts.  Of  this  kind  is  the  salt  called  cream  of  tartar. 

Caroline.  Is  not  the  salt  of  lemon,  commonly  used  to  take 
out  ink-spots  and  stains,  of  this  nature? 

j\lrs.  B.  No $  that  salt  consists  of  the  oxalic  acid,  combined 
with  a  little  potash.  It  is  found  in  that  state  in  sorrel. 

Caroline.  And  pray  how  does  it  take  out  ink-spots  ? 

Mrs.  B.  By  uniting  with  the  iron,  and  rendering  it  soluble 
in  water. 

Besides  the  vegetable  materials  which  we  have  enumerated, 
a  variety  of  other  substances,  common  to  tiie  three  kingdoms^ 
are  found  in  vegetables,  such  as  potash,  which  was  formerly 
supposed  to  belong  exclusively  to  plants,  *and  was,  in  conse- 
quence, called  the  vegetable  alkali. 

Sulphur,  phosphorus,  earths,  and  a  variety  of  metallic  oxyds, 
are  also  found  in  vegetables,  but  only  in  small  quantities.  And 
we  meet  sometimes  with  neutral  salts,  formed  by  the  combina- 
tion of  these  ingredients. 

23 


254  DECOMPOSITION 

CONVERSATION  XXL 

ON  THE  DECOMPOSITION  OF  VEGETABLES. 

Caroline.  THE  account  which  you  have  given  us,  Mrs.  B.5 
of  the  materials  of  vegetables,  is,  doubtless,  very  instructive  but 
ft  does  not  completely  satisfjlmy  curiosity.  I  wish  to  know  how 
plants  obtain  the  principles  from  which  their  various  materials 
are  formed  ;  by  what  means  these  are  converted  into  vegetable 
matter,  and  how  they  are  connected  with  the  life  of  the  plant  ? 

Mrs.  B.  This  implies  nothing  less  than  a  complete  history 
of  the  chemistry  and  physiology  of  vegetation,  subjects  on 
which  we  have  yet  but  very  imperfect  notions.  Still  I  hope 
that  I  shall  be  able,  in  some  measure,  to  satisfy  your  curiosity. 
But,  in  order  to  render  the  subject  more  intelligible,  I  must  first 
make  you  acquainted  with  the  various  changes  which  vegeta- 
bles undergo,  when  the  vital  power  no  longer  enables  them  to 
resist  the  common  laws  of  chemical  attraction. 

The  composition  of  vegetables  being  more  complicated  than 
that  of  minerals,  the  former  more  readily  undergo  chemical 
changes  than  the  latter :  for  the  greater  the  variety  of  attrac- 
tions, the  more  easily  is  the  equilibrium  destroyed,  and  a  new 
order  of  combinations  introduced. 

Emily.  I  am  surprised  that  vegetables  should  be  so  easily- 
susceptible  of  decomposition  ;  for  the  preservation  of  the  veg- 
*etable  kingdom  is  certainly  far  more  important  than  that  of 
minerals. 

Mrs.  B.  You  must  consider,  on  the  other  hand,  how  much 
more  easily  the  former  is  renewed  than  the  latter.  The  de- 
composition of  the  vegetable  takes  place  only  after  the  death  or" 
the  plant,  which,  in  the  common  course  of  nature,  happens 
when  it  has  yielded  fruit  and  seeds  to  propagate  its  species.  If. 
instead  of  thus  finishing  its  career,  each  plant  was  to  retain  its 
form  and  vegetable  state,. it  would  become  an  useless  burden  to 
the  eartli  and  its  inhabitants.  When  vegetables,  therefore, 
cease  to  be  productive,  they  cease  to  live,  and  nature  then  be- 
gins her  process  of  decomposition,  in  order  to  resolve  them  in- 
to their  chemical  constituents,  hydrogen,  carbon,  and  oxygen  ; 
those  simple  and  primitive  ingredients,  which  she  keeps  in  store 
for  all  her  combinations. 

Emily.  But  since  no  system  of  combination  can  be  destroy- 
ed, except  by  the  establishment  of  another  order  of  attractions, 
how  can  the  decomposition  of  vegetables  reduce  them  to  their 
simple  elements  ? 


OP   VEGETABLES.  253 

Mrs.  B.  It  is  a  very  long  process,  during  which  a  variety  of 
new  combinations  are  successively  established  and  successively 
destroyed;  but,  in  each  of  these  changes,  the  ingredients  of 
vegetable  matter  tend  to  unite  in  a  more  simple  order  of  com- 
pounds, till  they  are  at  length  brought  to  their  elementary  state, 
or  at  least,  to  their  most  simple  order  of  combinations.  Thus 
j'ou  will  fintl  that  vegetables  are  in  the  end  almost  entirely  re- 
duced to  water  and  carbonic  acid;  the  hydrogen  and  carbon 
dividing  the  oxygen  between  them,  so  as  to  form  with  it  these 
two  substances.  But  the  variety  of  intermediate  combinations 
that  take  place  during  the  several  stages  of  the  decomposition  of 
vegetables,  present  us  with  a  new  set  of  compounds,  well  wor- 
thy of  our  examination. 

Caroline.  How  is  it  possible  that  vegetables,  while  putrefy- 
ing, should  produce  any  thing  worthy  of  observation  ? 

Mrs.  B.  They  are  susceptible  of  undergoing  certain  changes 
before  they  arrive  at  the  state  of  putrefaction,  which  is  the  final 
term  of  decomposition;  and  of  these  changes  we  avail  ourselves 
for  particular  and  important  purposes.  But,  in  order  to  make 
you  understand  this  subject,  which  is  of  considerable  import- 
ance, I  must  explain  it  more  in  detail. 

The  decomposition  of  vegetables  is  always  attended  by  a 
violent  internal  motion,  produced  by  the  disunion  of  one  or- 
der of  particles,  and  the  combination  of  another.  This  is  call- 
ed FERMENTATION.  There  are  several  periods  at  which  this 
process  stops,  so  that  a  state  of  rest  appears  to  be  restored,  and 
the  new  order  of  compounds  fairly  established.  But,  unless 
means  be  used  to  secure  these  new  combinations  in  their  actual 
state,  their  duration  will  be  but  transient,  and  a  new  fermenta- 
tion will  take  place,  by  which  the  compound  last  formed  will  be 
destroyed;  and  another,  and  less  complex  order,  will  succeed. 

Emily.  The  fermentations,  then,  appear  to  be  only  the  suc- 
cessive steps  by  which  a  vegetable  descends  to  its  final  dissolu* 
tion. 

Mrs.  B.  Precisely  so.     Your  definition  is  perfectly  correct. 

Caroline.  And  how  many  fermentations,  or  new  arrange- 
ments, does  a  vegetable  undergo  before  it  is  reduced  to  its  sim- 
ple ingredients? 

Mrs.  B.  Chemists  do  not  exactly  agree  in  this  point ;  but 
there  are,  I  think,  four  distinct  fermentations,  or  periods,  at 
which  the  decomposition  of  vegetable  matter  stops  and  chan- 
ges its  course.  But  every  kind  of  vegetable  matter  is  not  equal- 
ly susceptible  of  undergoing  all  these  fermentations. 

There  are  likewise  several   circumstances  required  to  pro- 


256  DECOMPOSITION 

duce  fermentation.  Water  and  a  certain  degree  of  heat  ait 
both  essential  to  this  process,  in  order  lo  separate  the  particles, 
and  thus  weaken  their  force  of  cohesion,  that  the  new  chemic- 
al affinities  may  be  brought  into  action.  • 

Caroline.  In  frozen  climates,  then,  how  can  the  spontaneous 
decomposition  of  vegetables  take  place? 

Ms.  B.  It  certainly  cannot;  and,  accordingly,  we  find 
scarcely  any  vestiges  of  vegetation  where  a  constant  frost  pre- 
vails. 

Caroline.  One  would  imagine  that,  on  the  contrary,  such 
spots  would  be  covered  with  vegetables;  for,  since  they  cannot 
be  decomposed,  their  number  must  always  increase. 

Mrs.  B.  But,  my  dear,  heat  and  water  are  quite  as  essential 
to  the  formation  of  vegetables,  as  they  are  to  their  decomposi- 
tion. Besides,  it  is  from  the  dead  vegetables,  reduced  to  their 
elementary  principles,  that  the  rising  generation  is  supplied 
with  sustenance.  No  young  plant,  therefore,  can  grow  unless 
its  predecessors  contribute  both  to  its  formation  and  support  j 
and  these  not  oaly  furnish  the  seed  from  which  the  new  plant 
springs,  but  likewise  the  food  by  which  it  is  nourished. 

Caroline.  Under  the  torrid  zone,  therefore,  where  water  is 
never  frozen,  and  the  heat  is  very  great,  both  the  processes  of 
vegetation  and  of  fermentation  must,  I  suppose,  be  extremely 
rapid  ? 

Mrs.  B.  Not  so  much  as  you  imagine  :  for  in  such  climates 
great  part  of  the  water  which  is  required  for  these  processes  is 
in  an  aeriform  state,  which  is  scarcely  more  conducive  either  to 
the  growth  or  formation  of  vegetables  than  that  of  ice.  In 
those  latitudes,  therefore,  it  is  only  in  low  damp  situations,  shel- 
tered by  woods  from  the  sun's  rays,  that  the  smaller  tribes  of 
vegetables  can  grow  and  thrive  during  the  dry  season,  as  dead 
vegetables  seldom  retain  water  enoughrfo  produce  fermentation, 
but  are,  on  the  contrary,  soon  dried  up  by  the  heat  of  the  sun, 
which  enables  them  to  resist  that  process  :  so  that  it  is  not  till 
the  fall  of  the  autumnal  rains  (which  are  very  violent  in  such 
climates,)  that  spontaneous  fermentation  can  take  place. 

The  several  fermentations  derive  their  names  from  theii 
principal  products.  The  first  is  called  the  saccharine  ferment - 
ation,  because  its  product  is  sugar. 

Caroline.  But  sugar,  you  have  told  us,  is  found  in  all  vegeta- 
bles ;  it  cannot,  therefore,  be  the  product  of  their  decomposi- 
tion. 

Mrs.  B.  It  is  true  that  this  fermentation  is  not  cofined  to  the 
decomposition  of  vegetables,  as  it  continually  takes  place  during 
their  life;  and,  indeed,  this  circumstance  has,  till  lately,  pre~ 


OP    VEGETABLES.  257 

vented  it  from  being  considered  as  one  of  the  fermentations, 
But  the  process  appears  so  analogous  to  the  other  fermentations, 
and  the  formation  of  sugar,  whether  in  living  or  dead  vegetable 
matter  is  so  evidently  a  new  compound,  proceeding  from  the 
destruction  of  the  previous  order  of  combinations,  und  essential 
to  the  subsequent  fermentations,  that  it  is  now,  I  believe,  gene- 
rally esteemed  the  first  step,  or  necessary  preliminary,  to  de- 
composition, if  not  an  actual  commencement  of  that  process. 

Caroline.  I  recollect  your  hinting  to  us  that  sugar  was  suppo- 
sed not  to  be  secreted  from  the  sap,  in  the  same  manner  as  mu- 
cilage, fecula,  o9,  and  the  other  ingredients  of  vegetables. 

Mrs.  B.  It  is  rather  from  these  materials,  than  from  the  sap 
itself,  that  sugar  is  formed  ;  and  it  is  developed  at  particular 
periods,  as  you  may  observe  in  fruits,  which  become  sweet  in 
ripening,  sometimes  even  after  they  have  been  gathered.  Life, 
therefore,  is  not  essential  to  the  formation  of  sugar,  whilst  on 
the  contrary,  mucilage,  fecula,  and  the  other  vegetable  materials 
that  are  secreted  from  the  sap  by  appropriate  organs,  whose 
powers  immediately  depend  on  the  vital  principle,  cannot  bo 
produced  but  during  the  existence  of  that  principle. 

Emily.  The  ripening  of  Uiuits  is,  then,  their  first  step  to  de- 
struction, as  well  as  their  tast  Cowards  perfection  ? 

Mrs.  B.  Exactly. — A  process  analogous  to  the  saccharine 
fermentation  takes  place  also  during  the  cooking  of  certain  ve- 
getables. This  is  the  case  with  parsnips,  carrots,  potatoes,  &c. 
in  which  sweetness  is  developed  by  heat  and  moisture ;  and  we 
know  that  if  we  carry  the  process  a  little  farther,  a  more  com- 
plete decomposition  would  ensue.  The  same  process  takes 
place  also  in  seeds  previous  to  their  sprouting. 

Caroline.  How  do  you  reconcile  this  to  your  theory,  Mrs. 
B.  ?  Can  you  suppose  that  a  decomposition  is  the  necessary 
precursor  of  life  ? 

Mrs.  B.  That  is  indeed  the  case.  The  materials  of  the  seed 
must  be  decomposed,  and  the  seed  disorganized,  before  a  plant 
can  sprout  from  it.  Seeds,  besides  the  embrio  plant,  contain 
(as  we  have  already  observed)  fecula,  oil,  and  a  little  mucilage. 
These  substances  are  destined  for  the  nourishment  of  the  future 
plant ;  but  they  undergo  some  change  before  they  can  be  fit  for 
this  function.  The  seeds,  when  buried  in  the  earth,  with  a  cer- 
tain degree  of  moisture  and  of  temperature,  absorb  water, 
which  dilates  them,  separates  their  particles,  and  introduces  a 
new  order  of  attractions,  of  which  sugar  is  the  product.  The 
substance  of  the  seed  is  thus  softened,  sweetened,  and  converted 
into  a  sort  of  white  milky  pulp,  fit  for  the  nourishment  of  the 
embrio  plant. 

23* 


258  DECOMPOSITION 

The  saccharine  fermentation  of  seeds  is  artificially  produced, 
for  the  purpose  of  making  malt)  by  the  following  process  *-<-  A 
quantity  of  barley  is  first  soaked  in  water  for  two  or  three  days : 
the  water  being  afterwards  drained  off,  the  grain  heats  sponta- 
neously, swells,  bursts,  sweetens,  shows  a  disposition  to  germin- 
ate, and  actually  sprouts  to  the  length  of  an  inch,  when  the  pro- 
cess is  stopped  by  putting  it  into  a  kiln,  where  it  is  well  dried 
at  a  gentle  heat.  In  this  state  it  is  crisp  and  friable,  and  con- 
stitutes the  substance  called  malt,  which  is  the  principal  ingredi- 
ent of  beer. 

Emily.  But  I  hope  you  will  tell  us  how  malt  is  made  into 
beer? 

Mrs.  B.  Certainly ;  but  I  must  first  explain  to  you  the  na- 
ture of  the  second  fermentation,  which  is  essential  to  that  ope- 
ration. This  is  called  the  vinous  fermentation,  because  its  pro- 
duct is  wine. 

Etnily.  How  very  different  the  decomposition  of  vegetables 
is  from  what  I  had  imagined  !  The  pioducts  of  their  disorgani- 
sation appear  almost  superior  to  those  which  they  yield  during 
their  state  of  life  and  perfection. 

Mrs.  B.  And  do  you  not,  at  tht  s^me  time,  admire  the  beau- 
tiful economy  of  Niture,  which,  whether  she  creates,  or  wheth- 
Fer  she  destroys,  directs  all  her  operations  to  some  useful  snti 
benevolent  purpose  ? — It  appears  that  the  saccharine  fermenta- 
tisn  is  extremely  favourable,  if  not  absolutely  essential,  as  a 
previous  step,  to  the  vinous  fermentation  ;  so  that  if  sugar  be 
not  developed  'luring  the  life  of  the  plant,  the  saccharine  fer- 
mentation must  be  artificially  produced  before  the  vinous  fer- 
mentation can  take  place.  This  is  the  case  with  barley,  which 
does  not  yield  any  sugar  until  it  is  made  into  malt  5  and  it 
is  in  that  state  only  that  it  is  susceptible  of  undergoing  the  vi- 
nous fermentation  by  which  it  is  converted  into  beer. 

Caroline.  But  if  the  product  of  the  vinous  fermentation  is 
always  wine,  beer  cannot  have  undergone  that  process,  for  beer 
is  certainly  not  wine. 

Mrs.  B.  Chemically  speaking,  beer  may  be  considered  as 
the  wine  of  grain.  For  it  is  the  product  of  the  fermentation  of 
malt,  just  as  wine  is  that  of  the  fermentation  of  grapes,  or  other 
'fruits. 

The  consequence  of  the  vinous  fermentation  is  the  decompo- 
sition of  the  saccharine  matter,  and  the  formation  of  a  spiritu- 
ous liquor  from  the  constituents  of  the  sugar.  But,  in  order  to 
promote  this  fermentation,  net  only  water  and  a  certain  degree 
of  htat  are  necessary,  but  also  some  other  vegetable  ingredients, 
besides  the  sugar,  as  fecula,  mucilage,  acids,  salts,  extractive 
§ 


Of    VEGETABLES.  259 

matter,  &c.  all  of  which  seem  to  contribute  to  this  process ;  and 
give  to  the  liquor  its  peculiar  taste. 

Emily.  It  is,  perhaps,  for  this  reason  that  wine  is  notjobtain- 
ed  from  the  fermentation  of  pure  sugar ;  but  that  fruits  are  cho- 
sen for  that  purpose,  as  they  contain  not  only  sugar,  but  like- 
wise the  other  vegetable  ingredients  which  promote  the  vinous 
fermentation,  and  give  the  peculiar  flavour. 

Airs.  b.  Certainly.  And  you  must  observe  also,  that  the  re- 
lative quantity  of  sugar  is  not  the  only  circumstance  to  be  con- 
sidered in  the  choice  of  vegetable  juices  for  the  formation  of 
wine,  otherwise  the  sugar-cane  would  be  best  adapted  for  that 
purpose.  It  is  rather  the  manner  and  proportion  in  which  the 
sugar  is  mixed  with  other  vegetable  ingredients  that  influences 
the  production  and  qualities  of  wine.  And  it  is  found  that  the 
juice  of  the  grape  not  only  yi*!ds  the  most  considerable  propor- 
tion of  wine,  but  that  it  likewise  affords  it  of  the  most  grateful 
flavour. 

Emily.  I  have  seen  a  vintage  in  Switzerland,  and  I  do  not 
recollect  that  heat  was  applied,  or  water  added,  to  produce  the 
fermentation  of  the  grapes. 

Mrs.  />'.  The  common  temperature  of  the  atmosphere  in  the 
cellars  in  which  the  juice  of  the  grape  is  fermented  is  sufficiently 
warm  for  this  purpose;  and  as  the  juice  contains  an  ample  sup- 
ply of  water,  there  is  no  occasion  for  any  addition  of  it.  But 
when  fermentation  is  produced  in  dry  mSlt,  a  quantity  of  water 
must  necessarily  be  added. 

Emily.  But  what  are  precisely  the  changes  that  happen  du- 
ring the  vinous  fermentation  ? 

Mrs.  B.  The  sugar  is  decomposed,  and  its  constituents  are 
recombined  into  two  new  substances;  the  one  a  peculiar  liquid 
substance,  called  alcohol  or  spirit  of  wine,  which  remains  in 
the  fluid  ;  the  other,  carbonic  acid  gas,  which  escapes  during 
the  fermentation.  Wine,  therefore,  as  1  before  observed,  in  a 
general  point  of  view,  may  be  considered  as  a  liquid  of  which 
alcohol  constitutes  the  essential  part.  And  the  varieties  of 
strength  and  flavour  of  the  different  kinds  of  wine  are  to  be  at* 
tributed  to  the  different  qualti^es  of  the  fruits  from  which  they 
are  obtained,  independently  of  the  sugar. 

Caroline.  lam  astonished  to'  hear  that  so  powerful  a  liquid 
as  spirit  of  wine  should  be  obtained  from  so  mild  a  substance 
as  sugar. 

Airs.  B.  Can  you  tell  me  in  what  the  principal  difference 
consists  between  alcohol  and  sugar  ? 

Caroline.  Let  me  reflect  ....  Sugar  consists  of  carbon,  hy- 
drogen, and  oxygen.  If  carbonic  acid  be  subtracted  from  it? 


260  DECOMPOSITION 

during  the  formation  of  alcohol,  the  latter  will  contain  less  car- 
bon and  oxygen  than  sugar  does ;  therefore  hydrogen  must  be 
the  prevailing  principle  of  alcohol. 

Mrs.  B.  It  is  exactly  so.  And  this  very  large  proportion  of 
hydrogen  accounts  for  the  lightness  and  .combustible  property  of 
alcohol,  and  of  spirits  in  general,  all  of  which  consist  of  alcohol 
variously  modified. 

Emily.  And  can  sugar  be  recomposed  from  the  combination 
of  alcohol  and  carbonic  acrd  ? 

Mrs.  B.  Chemists  have  never  been  able  to  succeed  in  effect- 
ing this  ;  but  from  analogy,  I  should  suppose  such  a  recompo- 
sition  possible.  Let  us  now  observe  more  particularly  the  phe- 
nomena that  take  place  during  the  vinous  fermentaiion.  At  the 
commencement  of  this  process,  heat  is  evolved;  and  the  liquor 
swells  considerably  Iron)  -the  formation  of  the  carbonic  acid, 
which  is  disengaged  in  such  prodigious  quantities  as  would  be 
fatal  to  any  person  who  should  unawares  inspire  it  ;  an  acci- 
dent which  lias  sometimes  happened.  If  the  fermentation  be 
stopped  by  putting  the  liquor  into  barrels,  before  the  whole  of 
the  carbonic  acid  is  evolved,  the  wine  is  brisk,  like  Champagne, 
from  the  carbonic  acid  imprisoned  in  it,  and  it  tastes  sweet,  like 
cyder,  from  the  sugar  not  being  completely  decomposed. 

Emily.  But  I  do  not  understand  why  heat  should  be  evolved 
during  this  operation.  For,  as  there  is  a  considerable  forma- 
tion of  gas,  in  which  Ti  proportionable  quantity  of  heat  must 
become  insensible,  I  should  have  imagined  that  cold,  rather 
than  heat,  would  have  been  produced. 

Mrs.  B.  It  appears  so  on  first  consideration  ;  but  you  must 
recollect  that  fermentation  is  a  complicated  chemical  process  ; 
and  that,  during  the  decompositions  and  recompositions  atten- 
ding it,  a  quantity  of  chemical  heat  may  be  disengaged,  suffi- 
cient both  to  develope  the  gas,  and  to  effect  an  increase  of  tem- 
perature. When  the  fermentation  is  completed,  the  liquid 
cools  and  subsides,  the  effervescence  ceases,  and  the  thick, 
sweet,  sticky  juice  of  the  fruit  is  converted  into  a  clear,  trans- 
parent, spiritous  liquor,  called  wine. 

Emily.  How  much  I  regret  not  having  been  acquainted  with 
the  nature  of  the  vinous  fermentation,  when  I  had  an  opportu- 
nity of  seeing  the  process  ! 

Mrs.  B.  You  have  an  easy  method  of  satisfying  yourself  in 
that  respect  by  observing  the  process  of  brewing,  which,  in  eve- 
ry essential  circumstance,  is  similar  to  that  of  making  wine, 
and  is  really  a  very  curious  chemical  operation. 

Although  we  cannot  actually  make  wine  at  this  moment,  it 
will  be  easy  to  show  you  the  mode  of  analyzing  it  This  is 


OP   VEGETABLES.  2()1 

done  by  distillation.  When  wine  of  any  kind  is  submitted  to 
this  operation,  it  is  found  to  contain  brandy,  water,  tartar,  ex- 
tractive colouring  matter,  and  some  vegetable  acids.  I  have 
put  a  little  port  wine  into  this  alembic  of  glass  (PLATE  XIV. 
fig.  1.,)  and  on  placing  the  lamp  under  it,  you  will  soon  see  the 
spirit  and  water  successively  come  over — 

Emily.  But  you  do  not  mention  alcohol  amongst  the  pro* 
ducts  of  the  distillation  of  wine ;  and  yet  that  is  its  most  es- 
sential ingredient  ? 

Mrs.  B.  The  alcohol  is  contained  in  the  brandy  which  is  now 
coming  over,  and  dropping  from  the  still.  Brandy  is  nothing 
more  than  a  mixture  of  alcohol  and  water  ;  and  in,  order  to 
obtain  the  alcohol  pure,  we  must  again  distil  it  from  brandy. 

Caroline.  I  have  just  taken  a  drop  on  my  finger ;  it  tastes 
like  strong  brandy,  but  it  is  without  colour,  whilst  brandy  is 
of  a  deep  yellow. 

Mrs.  B.  It  is  not  so  naturally ;  in  its  pure  state  brandy  is 
colourless,  and  it  obtains  the  yellow  tint  you  observe,  by  ex- 
tracting the  colouring  matter  from  the  new  oaken  casks  in  which 
it  is  kept.  But  if  it  does  not  acquire  the  usual  tinge  in  this 
way,  it  is  the  custom  to  colour  the  brandy  used  in  this  country 
artificially,  with  a  little  burnt  sugar,  in  order  to  give  it  the  ap- 
pearance of  having  been  long  kept. 

Caroline.  And  is  rum  also  distilled  from  wine  ? 

Mrs.  B.  By  no  means  ;  it  is  distilled  from  the  sugar-cane,  a 
plant  which  contains  so  great  a  quantity  of  sugar,  that  it  yields 
more  alcohol  than  almost  any  other  vegetable.  After  the  juice 
of  the  cane  has  been  pressed  out  for  making  sugar,  what  still 
remains  in  the  bruised  cane  is  extracted  by  water,  and  this  wa- 
tery solution  of  sugar  is  fermented,  and  produces  rum. 

The  spirituous  liquor  called  arack  is  in  a  similar  manner  dis* 
tilled  from  the  product  of  the  vinous  fermentation  of  rice. 

Emily.  But  rice  has  no  sweetness  ;  does  it  contain  any  su- 
gar ? 

Airs.  B.  Like  barley  and  most  other  seeds,  it  is  insipid  until 
it  has  undergone  the  saccharine  fermentation ;  and  this,  you 
must  recollect,  is  always  a  previous  step  to  the  vinous  fermenta- 
tion in  those  vegetables  in  which  sugar  is  not  already  formed. 
Brandy  may  in  the  same  manner  be  obtained  from  malt. 

Caroline.  You  mean  from  beer,  I  suppose ;  for  the  malt 
must  have  previously  undergone  the  vinous  fermentation. 

Mrs.  B.  Beer  is  not  precisely  the  product  of  the  vinous  fer- 
mentation of  malt.  For  hops  are  a  necessary  ingredient  for  the 
formation  of  that  liquor  ;  whilst  brandy  is  distilled  from  pure 


262  DECOMPOSITION 

fermented  malt.  But  brandy  might,  no  doubt,  be  distilled  from 
beer  as  well  as  from  any  other  liquor  that  has  undergone  the 
vinous  fermentation  ;  for  since  the  basis  of  brandy  is  alcohol,  it 
may  be  obtained  from  any  liquid  that  contains  that  spirituous 
substance. 

Emily.  And  pray,  from  what  vegetable  is  the  favourite  spi- 
rit of  the  lower  orders  of  the  people,  gin,  extracted  ? 

Mrs.  B.  The  spirit  (which  is  the  same  in  alt  fermented  li- 
quors) may  be  obtained  from  any  kind  of  grain  ;  but  the  pe- 
culiar flavour  which  distinguishes  gin  is  that  of  juniper  berries, 
which  are  distilled  together  with  the  grain — 

I  think  the  brandy  contained  in  the  wine  we  are  distilling 
must,  by  this  time,  be  all  come  over.  Yes — taste  the  liquid 
that  is  now  dropping  from  the  alembic — 

Caroline.  It  is  perfectly  insipid,  like  water. 

Mrs.  B.  It  is  water,  which,  as  I  was  telling  you,  is  the  se- 
«?ond  product  of  wine,  and  comes  over  after  all  the  spirit,  which 
is  the  lightest  part,  is  distilled. — The  tartar  and  extractive  col- 
ouring matter  we  shall  find  in  a  solid  form  at  the  bottom  of  the 
alembic. 

Emily.  They  look  very  like  the  lees  of  wine. 

Mrs.  B.  And  in  many  respects  they  are  of  a  similar  nature, 
for  lees  of  wine  consist  chiefly  of  tartrit  of  potash  ;  a  salt  which 
exists  in  the  juice  of  the  grape,  and  in  many  other  vegetables, 
and  is  developed  only  by  the  vinous  fermentation.  During  this 
operation  it  is  precipitated,  and  deposils  itself  on  the  internal 
surface  of  the  cask  in  which  the  wine  is  contained.  It  is  much 
used  in  medicine,  and  in  various  arts,  particularly  dying,  under 
the  name  of  cream  of  tartar,  and  it  is  from  this  salt  that  the 
tartarous  acid  is  obtained. 

Caroline.  But  the  medicinal  cream  of  tartar  is  in  appearance 
quite  different  from  these  dark-coloured  dregs  ;  it  is  perfectly 
colourless. 

Mrs.  B.  Because  it  consists  of  the  pure  salts  only,  in  its  crys- 
tallised form  ;  whilst  in  the  instance  before  us  it  is  mixed  with 
the  deep-coloured  extractive  matter,  and  other  foreign  ingredi- 
ents. 

Emily.  Pray  cannot  we  now  obtain  pure  alcohol  from  the 
brandy  which  we  have  distilled  ? 

Mrt.  B.  We  might ;  but  the  process  would  be  tedious  ;  for 

in  order  to  obtain  alcohol  perfectly  free  from  water,  it  is  neces- 

,sary  to  distil,  or,  as  the  distillers  call  it,  rectify  it  several  times. 

You  must  therefore  allow  me  to  produce  a  bottle  of  alcohol  that 

has  been  thus  purified.     This  is  a  very  important  ingredient. 


OE    VEGETABLES.  l'0o 

which  has  many  striking  properties,  besides  its  forming  the  ba- 
sis of  all  spirituous  liquors. 

Emily.  It  is  alcohol,  I  suppose,  that  produces  intoxication  ? 

Mrs.  B.  Certainly  ;  but  the  stimulus  and  momentary  energy 
it  gives  to  the  system,  and  the  intoxication  it  occasions  when 
taken  in  excess,  are  circumstances  not  yet  accounted  for. 

Caroline.  I'thought  that  it  produced  these  effects  by  increas- 
ing the  rapidity  of  the  circulation  of  the  blood  ;  for  drinking 
wine  or  spirits,  I  have  heard,  always  quickens  the  pulse. 

Mrs.  B.  No  doubt  ;  the  spirit,  by  stimulating  the  nerves, 
increases  the  action  of  the  muscles  ;  and  the  heart,  which  is 
one  of  the  strongest  muscular  organs,  beats  with  augmented  vi- 
gour, and  propels  the  blood  with  accelerated  quickness,  After 
such  a  strong  excitation,  the  frame  naturally  suffers  a  propor- 
tional degree  of  depression,  so  that  a  state  of  debility  and  lan- 
guor is  the  invariable  consequence  of  intoxication.  Cut  though 
these  circumstances  are  well  ascertained,  they  aie  far  from  ex- 
plaining why  alcohol  should  produce  such  effects. 

Emily.  Liquers  are  the  only  kind  of  spirits  which  I  think 
pleasant.  Pray  of  what  do  they  consist  ? 

Mrs.  B.  They  are  composed  of  alcohol,  sweetened  with  sy- 
rup, and  flavoured  with  volatile  oil. 

The  different  kinds  of  odoriferous  spirituous  waters  are  like- 
wise solutions  of  volatile  oil  in  alcohol,  as  lavender  water,  eau 
de  Cologne,  &c. 

The  chemical  properties  of  alcohol  are  important  and  nume- 
rous. It  is  one  of  the  most  powerful  chemical  agents,  and  is 
particularly  useful  in  dissolving  a  variety  of  substances,  which 
are  soluble  neither  by  water  nor  heat. 

Emily.  We  have  seen  it  dissolve  copal  and  mastic  to  form 
varnishes  ;  and  these  resins  are  certainly  not  soluble  in  water, 
since  water  precipitates  them  from  their  solution  in  alcohol. 

Mrs.  B.  1  am  happy  to  find  that  you  recollect  these  circum- 
stances so  well.  The  same  experinKMt  affords  also  an  instance 
of  another  property  of  alcohol, — its  tendency  to  unite  with  wa- 
ter; for  the  resin  is  precipitated  in  consequence  of  losing  the  al- 
cohol, which  abandons  it  from  its  preference  for  water.  It  is 
attended  also,  as  you  may  recollect,  with  the  same  peculiar  cir- 
cumstance of  a  disengagement  of  heat  and  consequent  diminu- 
tion of  bulk,  which  we  have  supposed  to  be  produced  by  a  me- 
chanical penetration  of  particles  by  which  latent  heat  is  forced 
out. 

Alcohol  unites  thus  readily  not  only  with  resins  and  with 
water,  but  with  oils  and  balsams ;  these  compounds  form  th^ 
extensive  class  of  elixirs,  tinctures,  quintessences,  &c, 


264  DECOMPOSITION 

Emily.  I  suppose  that  alcohol  must  be  highly  combustible, 
since  it  contains  so  large  a  proportion  of  hydrogen  ? 

Mrs.  B.  Extremely  so ;  and  it  will  burn  at  a  very  moderate 
temperature. 

Caroline.  I  have  often  seen  both  brandy  and  spirit  of  wine 
burnt;  they  produce  a  great  deal  of  flame,  but  not  a  propor- 
tional quantity  of  heat,  and  no  smoke  whatever. ' 

Mrs.  ti.  The  last  circumstance  arises  from  their  combus- 
tion being  complete;  and  the  disproportion  between  the  flame 
and  heat  shows  you  that  these  are  by  no  means  synonymous. 

The  great  quantity  of  flame  proceeds  from  the  combustion  of 
the  hydrogen  to  which  you  know,  that  manner  of  burning  is  pe- 
culiar.— Have  you  not  remarked  also  that  brandy  and  alcohol 
will  burn  without  a  wick? — They  take  fire  at  so  low  a  tempe- 
rature, that  this  assistance  is  not  required  to  concentrate  the 
heat  and  volatilise  the  fluid. 

Caroline.  1  have  sometimes  seen  brandy  burnt  by  merely 
heating  it  in  a  spoon. 

Mrs.  B.  The  rapidity  of  the  combustion  of  alcohol  may, 
however,  be  prodigiously  increased  by  first  volatilising  it.  An 
ingenious  instrument  has  been  constructed  on  this  principle  to 
answer  the  purpose  of  a  blow-pipe,  which  may  be  used  for 
melting  glass,  or  other  chemical  purposes.  It  consists  of  a 
small  metallic  vessel  (PLATE  XIII.  fig.  2.)  of  a  spherical  shape, 
which  contains  the  alcohol,  and  is  heated  by  the  lamp  beneath 
it;  as  soon  as  the  alcohol  is  volatilised,  it  passes  through  the 
spout  of  the  vessel,  and  issues  just  above  the  wick  of  the  lamp, 
which  immediately  sets  fire  to  the  stream  of  vapour  as  I  shall 
show  you — * 

Emily.  With  what  amazing  violence  it  burns !  The  flame  of 
alcohol,  in  the  state  of  vapour,  is,  I  fancy,  much  hotter  than 
when  the  spirit  is  merely  burnt  in  a  spoon? 

Mrs.  B.  Yes  ;  because  in  tbis  way  the  combustion  goes  on 
much  quicker,  and,  of  course,  the  heat  is  proportionally  increa- 
sed.— Observe  its  effect  on  this  small  glass  tube,  the  middle  of 
which  1  present  to  the  extremity  of  the  flame,  where  the  heat 
is  gieatest. 

*  A  spirit  lamp,  which  answers  very  well  for  bending  small  glass 
tubes,  may  be  constructd  by  almost  any  one.  Take  a  lo  vial  with 
a  wide  mouth,  fit  a  coric  to  it  and  pierce  tne  cork  to  admit  a  piece  of 
glass  tube,  the  bore  of  which  is  about  the  size  o(  a  large  gooscquill. 
Let  the  tube  lise  an  inch  or  two  above  the  cork — pass  some  cotton 
wick  through  the  tube — then  fill  the  vial  with  alcohol  and  put  the  cork 
and  tube  in  their  places.  The  lamp  is  then  ready.  C. 


OF    VEGETABLES. 

Caroline.  The  glass,  in  that  spot,  is  become  red  hot,  and 
bends  from  its  own  weight. 

./WAV.  B.  1  have  not  drawn  it  asunder,  and  am  going  to  blow 
a  ball  at  one  of  the  heated  ends  :  but  I  must  previously  close  it 
up,  and  flatten  it  with  this  little  metallic  instrument,  otherwise 
the  breath  would  pass  through  the  tube  without  dilating  any 
part  of  it. — Now  Caroline,  will  you  blow  strongly  into  the  tube 
whilst  the  closed  end  is  red  hot. 

Emily.  You  biowed  too  hard ;  for  the  ball  suddenly  dilated 
to  a  great  size,  and  then  burst  in  pieces.  > 

Mrs.  B.  You  will  be  more  expert  another  time;  but  I  must 
caution  you,  should  you  ever  use  this  blow-pipe,  to  be  very 
careful  that  the  combustion  of  the  alcohol  does  not  go  on  with 
too  great  violence,  for  I  have  seen  the  flame  sometimes  dart  out 
with  such  force  as  to  reach  the  opposite  wall  of  the  room,  and 
set  the  paint  on  fire.  There  is,  however,  no  danger  of  the  ves- 
sel bursting,  as  it  is  provided  with  a  safety  tube,  which  affords 
an  additional  vent  for  the  vapour  of  alcohol  when  required. 

The  products  of  the  combustion  of  alcohol  consist  in  a  great 
proportion  of  water,  and  a  small  quantity  of  carbonic  acid. 
There  is  no  smoke  or  fixed  remains  whatever. — How  do  you 
account  for  that,  Emily  ? 

Emily.  I  suppose  that  the  oxygen  which  the  alcohol  absorbs 
in  burning,  converts  its  hydrogen  into  water  and  its  carbon  h> 
to  carbonic  acid  gas,  and  thus  it  is  completely  consumed. 

J\1rs.  B.  Very  well. — Ether,  the  lightest  of  all  fluids,  and 
with  which  you  are  well  acquainted,  is  obtained  from  alcoholj 
of  which  it  forms  the  lightest  and  most  volatile  part. 

Emily.  Eether,  thn,  is  to  alcohol,  what  alcohol  is  to  brandy  r 

Mrs.  B.  No :  there  is  an  essential  difference.  In  order  to 
obtain  alcohol  from  brandy,  you  need  only  deprive  the  latter 
of  its  water ;  but  for  the  formation  of  ether,  the  alcohol  must 
be  decomposed,  and  one  of  its  constituents  partly  subtracted 
I  leave  you  to  guess  which  of  them  it  is— 

Emily.  It  cannot  be  hydrogen,  as  ether  is  more  volatile  than 
alcohol,  and  hydrogen  is  the  lightest  of  all  its  ingredients*  nor 
do  I  suppose  that  it  can  be  oxygen,  as  alcohol  contains  so  small 
i\  proportion  of  that  principle;  it  is,  therefore,  most  probably, 
carbon,  a  diminution  of  which  would  not  fail  to  render  the  new 
compound  more  volatile. 

Mrs.  B.  You  are  perfectly  right.  The  formation  of  ether 
consists  simply  L.  subtracting  from  the  alcohol  a  certain  pro- 
portion of  carbon  ;  this  is  effected  by  the  action  q^the  sul- 
phuric, nitric,  or  muriatic  acids,  on  a!r«?hol.  The  acid  and 
carbon  remain  at  the  bottom  of  the  vessel,  whilst  the  decarbor 

24 


266  DECOMPOSITION 

nised  alcohol  flies  off  in  the  form  of  a  condensable  vapour, 
which  is  ether. 

Ether  is  the  most  inflammable  of  all  fluids,  and  burns  at  so 
low  a  temperature  that  the  heat  evolved  during  its  combustion 
is  more  than  is  required  for  its  support,  so  that  a  quantity  of 
ether  is  volatilised,  which  takes  fire,  and  gradually  increases 
the  violence  of  the  combustion. 

Sir  Humphry  Davy  hr.s  lately  discovered  a  very  singular 
fact  respecting  the  vapour  of  ether.  If  a  few  drops  of  ether 
be  poured  into  a  wine-glass,  and  a  fine  platina  wire,  heated  al- 
most to  redness,  be  held  suspended  in  the  glasj,  close  to  the 
surface  of  the  ether,  the  wire  soon  becomes  intensely  red-hot, 
and  remains  so  for  any  length  of  time.  We  may  easily  try 
the  experiment 

Caroline.  How  very  curious !  The  wire  is  almost  white 
hot,  and  a  pungent  smell  rises  from  the  glass.  Pray  how  u; 
this  accounted  for  ? 

Jl/rs.  B.  This  is  owing  to  a  very  peculiar  property  of  the 
vapour  of  ether,  and  indeed  of  many  other  combustible  gaseous 
bodies.  At  a  certain  temperature  lower  than  that  of  ignition, 
these  vapours  undergo  a  slow  and  imperfect  combustion,  which 
does  not  give  rise,  in  any  sensible  degree,  to  the  phenomena  of 
light  and  flame,  and  yet  extricates  a  quantity  of  caloric  sufficient 
to  react  upon  the  wire  and  make  it  red-hot,  and  the  wire  in  its 
turn  keeps  up  the  effect  as  Jong  as  the  emission  of  vapour  con- 
tinues. 

This  singular  effect,  which  is  also  produced  by  alcohol,  may 
be  rendered  more  striking,  and  kvpt  up  for  an  indefinite  length 
of  time,  by  rolling  a  few  coils  of  platina  wire,  of  the  diameter  of 
from  about  1-COth  to  l-70th  of  an  inch,  round  the  wick  of  a 
spirit-lamp.  If  this  lamp  be  lighted  for  a  moment,  and  blown 
out  again,  the  wire,  after  ceasing  for  an  instant  to  be  luminous, 
becomes  red- hod  again,  though  the  lamp  is  extinguished,  and 
remains  glowing  vividly,  till  the  whole  of  the  spirit  contained  in 
the  lamp  has  been  evaporated  and  consumed  in  this  peculiar 
maffher. 

Caroline.  That  is  extremely  curious.  But  why  should  not 
an  iroti  or  silver  wire  produce  the  same  effect  ? 

Mrs.  B.  Because  either  iron  or  silver,  being  much  better 
conductors  of  heat  than  platina,  the  heafis  carried  off  too  fast 
by  those  metals  to  allow  the  accumulation  of  caloric  necessary 
to  produce  the  effect  in  question. 

Ether  is  so  light  that  it  evaporates  at  the  common  tempera- 
ture of  the  atmosphere;  it  is  therefore  necessary  to  keep  it  con- 


OF    VEGETABLES.  26f 

fined  by  a  well  ground  glass  stopper.     No  degree  of  cold  known 
has  ever  frozen  it.* 

Caroline.  Is  it  not  often  taken  medicinally  ? 

Mrs.  B.  Yes ;  it  is  one  of  the  most  effectual  antispasmodic 
medicines,  and  the  quickness  of  its  effects,  as  such,  probably  de- 
pends on  its  being  instantly  converted  into  vapour  by  the  heat 
of  the  stomach,  through  the  interventiou  of  which  it  acts  on  the 
nervous  system.  But  the  frequent  use  of  ether,  like  that  of 
spirituous  liquors,  becomes  prejudicial,  and,  if  taken  to  excess, 
ft  produces  effects  similar  to  those  of  intoxication. 

We  may  now  take  our  leave  of  the  vinous  fermentation,  of 
which  I  hope,  you  have  acquired  a  clear  idea  ;  as  well  as  of  the 
several  products  that  are  derived  from  it. 

Caroline.  Though  this  process  appears,  at  first  sight,  so  much 
complicated,  it  may,  I  think,  be  summed  up  in  a  few  words,  as 
it  consists  in  the  conversion  of  sugar  and  fermentable  bodies  in- 
to alcohol  and  carbonic  acid,  which  give  rise  both  to  the  forma- 
tion of  wine,  and  of  all  kinds  of  spirituous  liquors. 

Mrs.  B.  We  shall  now  proceed  to  the  acetous  fermentation^ 
which  is  thus  called,  because  it  converts  wine  into  vinegar, 
by  the  formation  of  the  acetous  acid,  which  is  the  basis  or  rad- 
ical of  vinegar. 

Caroline.  But  is  not  the  acidifying  principle  of  the  acetous 
acid  the  same  as  that  of  all  other  acids,  oxygen? 

Mrs.  B.  Certainly  ;  and  on  that  account  the  contact  of  air  is 
essential  to  this  fermentation, 'as  it  affords  the  necessary  supply 
of  oxygen.  Vinegar,  in  order  to  obtain  pure  acetous  acid  from 
it,  must  be  distilled  and  rectified  by  certain  processes. 

Emily.  But  pray,  Mrs.  B.,  is  not  the  acetous  acid  frequently 
formed  without  this  fermentation  taking  place  ?  Is  it  not,  for  in- 
stance, contained  in  acid  fruits/and  in  every  substance  that  be- 
comes sour  ? 

<\jrs.  B.  No,  not  in  fruits;  you  confound  it  with  the  citric, 
the  malic,  the  oxalic,  and  other  vegetable  acids,  to  which  living 
vegetables  owe  theiu  acidity.  But  whenever  a  vege  able  sub- 
stance turns  sour,  after  it  has  ceased  to  live,  the  acetous  acid  is 
developed  by  means  of  the  acetous  fermentation,  in  which  the 
substance  advances  a  step  towards  its  final  decomposition. 

Amongst  the  various  instances  of  acetous  fermentation,  that 
of  bread  is  usually  classed. 

Caroline.  But  the  fermentation  of  bread  is  produced  by  yeast ; 
how  does  that  effect  it  ? 

*  Ether freezes,  and  shoots  into  crystals  at  46°  below  the  zero  of 
Fftbrenhei!  ' ' 


DECOMPOSITION 


Mrs.  B.  It  is  found  by  experience  that  any  substance  that 
lias  already  undergone  a  fermentation,  will  readily  excite  it  in 
one  that  is  susceptible  of  that  process.  If,  for  instance,  yon 
mix  a  little  vinegar  with  wine,  that  is  intended  to  be  acidified, 
it  will  absorb  oxygen  more  rapidly,  and  the  process  be  com- 
pleted much  sooner,  than  if  left  to  ferment  spontaneously. 
Thus  yeast,  which  is  a  product  of  the  fermentation  of  beer,  is 
used  to  excite  and  accelerate  the  fermentation  of  malt,  which  is 
to  be  con  verted  into  beer,  as  well  as  that  of  paste  which  is  to  be 
made  into  bread. 

Caroline.  But  if  bread  undergoes  the  acetous  fermentation, 
why  is  it  not  sour  ? 

S.lrs.  B.  It  acquires  a  certain  savour  which  corrects  the  hea- 
vy insipidity  of  flour,  and  may  b*  reckoned  a  first  degree  of 
acidification  ;  or  if  the  process  were  carried  further,  the  bread 
would  become  decidedly  acid. 

There  are,  however,  some  chemists  who  do  not  consider  the 
fermentation  of  bread  as  being  of  the  acetous  kind,  but  suppose 
that  it  is  a  process  of  fermentation  peculiar  to  that  substance. 

Tbe  putrid  fermentation  is  the  final  operation  of  Nature,  and 
her  last  step  towards  reducing  organised  bodies  to  their  simplest 
combinations.  All  vegetables  spontaneously  undergo  this  fer- 
mentation after  death,  provided  there  be  a  sufficient  degree  of 
heat  and  moisture,  together  with  access  of  air  ;  for  it  is  well 
known  that  dead  plants  may  be  preserved  by  drying,  or  by  the 
total  exclusion  of  air. 

Caroline.  But  do  dead  plants  undergo  the  other  fermentation 
previous  to  this  last  ;  or  do  they  immediately  suffer  the  putrid 
fermentation  ? 

Mrs.  B.  That  depends  on  a  variety  of  circumstances,  such  as 
the  degrees  of  temperature  and  of  moisture,  the  nature  of  the 
plant  itself,  &c.  But  if  you  were  carefully  to  follow  and  exa- 
mine the  decomposition  of  plants  from  their  death  to  their  final 
dissolution,  you  would  generally  find  a  sweetness  developed,  in 
the  seeds,  and  a  spirituous  flavour  in  the  fruits  (which  have  un- 
dergone the  saccharine  fermentation),  previous  to  the  total  dis- 
organisation and  separation  of  the  parts. 

Emily.  I  have  sometimes  remarked  a  kind  of  spirituous  taste 
in  fruits  that  were  over  ripe,  especially  oranges;  and  this  was 
just  before  they  became  rotten. 

Airs.  B.  It  was  then  the  vinous  fermentation  which  had  suc- 
ceeded the  saccharine,  and  had  you  followed  up  these  changes 
attentively,  you  would  probably  have  found  the  spiritous  taste 
followed  by  acidity,  previous  to  the  fruit  passing  to  the  state  of 
putrefaction. 


OP    VEGlU'ABLES.  269 

When  the  leaves  fall  from  the  trees  in  autumn,  they  do  not 
Jf  there  is  no  great  moisture  in  the  atmosphere)  immediately 
undergo  a  decomposition,  but  are  first  dried  and  withered  ;  as 
soon,  however,  as  the  rain  sets  in,  fermentation  commences, 
their  gaseous  products  are  imperceptibly  evolved  into  the  at- 
mosphere, and  their  fixed  remains  mixed  with  their  kindred 
earth. 

Wood,  when  exposed  to  moisture,  also  undergoes  the  putrid 
fermentation  and  becomes  rotten. 

Emily.  But  I  have  heard  that  the  dry  rot,  which  is  so  liable 
to  destroy  the  beams  of  houses,  is  prevented  by  a  current  of  air; 
and  yet  you  said  that  air  was  essential  to  the  putrid  fermenta- 
tion ? 

Sifrs.  B.  True  ;  but  it  must  not  be  in  such  a  proportion  to 
the  moisture  as  to  dissolve  the  latter,  and  this  is  generally  the 
case  when  the  rotting  of  wood  is  prevented  or  stopped  by  the 
free  access  of  air.  What  is  commonly  called  dry  rot,  howev- 
er, is  •not  I  believe  a  true  process  of  putrefaction.  It  is  suppo- 
sed to  depend  on  a  peculiar  kind  of  vegetation,  which,  by  feed- 
ing on  the  wood,  gradually  destroys  it. 

Straw  and  all  other  kinds  of  vegetable  matter  undergo  th£ 
putird  fermentation  more  rapidly  when  mixed  with  animal  mat- 
ter. Much  heat  is  evolved  during  this  process,  and  a  variety 
of  volatile  products  are  disengaged,  as  carbonic  acid  arid  hy- 
drogen gas,  the  latter  of  which  is  frequently  either  sulphurated 
or  phosphorated. — When  nil  these  gases  have  been  evolved, 
the  fixed  products,  consisting  of  carbon,  salts,  potash,  &c.  form 
a  kind  of  vegetable  earth,  which  makes  very  fine  manure,  as 
it  is  composed  of  those  elements  which  form  the  immediate 
materials  of  plants. 

Caroline.  Pray  are  not  vegetables  sometimes  preserved  from 
decomposition  by  petrification  ?  I  have  seen  very  curious  spe- 
cimens of  petrified  vegetables,  in  which  state  they  perfectly 
preserve  their  form  and  organisation,  though  in  appearance 
they  are  changed  to  stone. 

Mrs.  B.  That  is  a  kind  of  metamorphosis,  which,  now  that 
you  are  tolerably  well  versed  in  the  history  of  mineral  and  veg- 
etable substances,  I  leave  to  your  judgment  to  explain.  Do 
you  imagine  that  vegetables  can  be  converted  into  stone? 

Emily.  No,  certainly ;  but  they  might  perhaps  be  changed 
*o  a  substance  in  appearance  resembling  stone. 

Mrs.  B.  It  is  not  so,  however,  with  the  substances  that  are 
called  petrified  vegetables  ;  for  these  are  really  stone,  and  gea~ 
24* 


erally  of  the  hardest  kind,  consisting  chiefly  of  silex.*  Tilt 
case  is  this ;  when  a  vegetable  is  buried  under  water,  or  in  wet 
earth,  it  is  slowly  and  gradually  decomposed.  As  each  suc- 
cessive particle  of  the  vegetable  is  destroyed,  its  place  is  sup- 
plied by  a  particle  of  siliceous  earth,  conveyed  thither  by  the 
water.  In  the  course  of  time  the  vegetable  is  entirely  destroy- 
ed, but  the  silex  has  completely  replaced  it,  having  assumod  its 
form  and  apparent  texture,  as  if  the  vegetable  itself  were  chan- 
ged to  stone. 

Caroline.  That  is  very  curious  !  and  I  suppose  that  petrifi- 
ed  animal  substances  are  of  the  same  nature  ? 

J\irs.  Bf  Precisely.  It  is  equally  impossible  for  either  ani- 
mal or  vegetable  substances  to  be  converted  into  stone.  They 
may  be  reduced,  as  we  find  they  are,  by  decomposition,  to  their 
constituent  elements,  but  cannot  be  changed  to  elements,  which 
dt5  not  enter  into  their  composition. 

There  are,  however,  circumstances  which  frequently  pre- 
vent the  regular  and  final  decomposition  of  vegetables;  as, 
for  instance,  when  they  are  buried  either  in  the  sea,  or  in  the 
earth,  where  they  cannot  undergo  the  putrid  fermenation  for 
want  of  air.  In  these  cases  they  are  subject  to  a  peculiar 
change,  by  which  they  are  converted  into  a  new  class  of  com- 
pounds, called  bitumens. 

Caroline.  These  are  substances  I  never  heard  of  before. 

Jk/rs.  l>.  You  will  find,  however,  that  some  of  them  are  very 
familiar  to  vou.  Bitumens  are  vegetables  so  far  decompo* 
sed  as  to  retain  no  organic  appearance  ;  but  their  origin  is 
easily  detected  by  their  oily  nature,  their  combustibility,  the  pro- 
ducts of  their  analysis,  and  the  impression  of  the  forms  oi 
leaves,  grains,  fibres  of  wood,  and  even  of  animals,  which  thev 
frequently  bear. 

They  are  sometimes  of  an  oily  liquid  consistence,  as  the  sub- 
stance called  naptha,*  in  which  we  preserved  potassium  ;  it  is 
a  fine  transparent  colourless  fluid,  that  issues  out  of  clays  in 
some  parts  of  Persia.  But  more  frequently  bitumens  are  solid, 
as  osphaltum,  a  smooth,  hard,  brittle  substance,  which  easily 
melts,  and  forms,  in  its  liquid  state,  a  beautiful  dark  brown  col- 
our for  oil  painting.  Jet,  which  is  of  a  still  harder  texture,  is 
a  peculiar  bitumen,  susceptible  of  so  fine  a  polish,  that  it  is 
used  for  many  ornamental  purposes. 

*  Petrifactions  arc  of  two  Kinds,  viz.  silecious,  when  flinty  particles 
take  the  place  of  the  original  substance,  and  calcareous  where  the  sub- 
stance appears  to  be  channel  to  li an  -stone.  The  first  kind  give0,  fire 
steel,  antrHhe  other  effervesces  with  acids.  C, 


OF    VEGETABLES.  27i 

Coal  is  also  a  bituminous  substance,  to  the  composition  of 
which  both  the  mineral  and  animal  kingdoms  seem  to  concur. 
This  most  useful  mineral  appears  to  consist  chiefly  of  vegetable 
matter,  mixed  with  the  remains  of  marine  animals  and  marine 
salts,  and  occasionally  containing  a  quantity  of  sulphuret  of 
iron,  commonly  called  pyrites. 

Emily.  It  is,  I  suppose,  the  earthy,  the  metallic,  and  the  sa- 
line parts  of  coals,  that  compose  the  cinders  or  fixed  products 
of  their  combustion  ;  whilst  the  hydrogen  and  carbon,  which 
they  derive  from  vegetables,  constitute  their  volatile  products. 

Caroline.  Pray  is  not  co/te,  (which  1  have  heard  is?  much 
used  in  some  manufactures,)  also  a  bituminous  substance? 

Mrs.  B.  No  ;  it  is  a  kind  of  fuel  artificially  prepared  from 
coals.  It  consists  of  coals  reduced  to  a  substance  analogous  to 
charcoal,  by  the  evaporation  of  their  bituminous  parts.  Coke, 
therefore,  is  composed  of  carbon,  with  some  earthy  and  saline 
ingredients. 

o«ccm,  or  yellow  amber,  is  a  bitumen  which  the  ancients 
called  elect  rum,  from  whence  the  word  electricity  is  derived,  as 
that  substance  is  peculiarly,  and  was  once  supposed  to  be  ex- 
clusively, electric.  It  is  found  either  deeply  buried  in  the  bow- 
els of  the  earth,  or  floating  on  the  sea,  and  is  supposed  to  be  a 
resinous  body  which  has  been  acted  on  by  sulphuric  acid,  as  its 
analysis  shows  it  to  consist  of  an  oil  and  an  acid.  The  oil  is 
called  oil  of  amber,  the  acid  the  siiccinic. 

Emily.  That  oil  I  have  sometimes  used  in  painting,  as  it  is 
reckoned  to  change  less  than  the  other  kinds  of  oils. 

Mrs.  B.  The  last  class  of  vegetable  substances  that  have 
changed  their  nature  are  fossil-wood,  peat,  and  turf.  These 
are  composed  of  wood  and  roots  of  shrubs,  that  are  partly  de- 
composed by  being  exposed  to  moisture  under  ground,  and  yet, 
in  some  measure,  preserve  their  form  and  organic  appearance. 
The  peat,  or  black  earth  of  the  moors,  retains  but  few  vestiges 
of  the  roots  to  which  it  owes  its  richness  and  combustibility, 
these  substances  being  in  the  course  of  time  reduced  to  the  state 
of  vegetable  earth.  But  in  turf  th«  roots  of  plants  are  still  dis- 
cernible, and  it  equally  answers  the  purpose  of  fuel.  It  is  the 
combustible  used  by  the  poor  in  heathy  countries,  which  supply* 
it  abundantly. 

*  Naptha  appears  to  be  the  only  fluid  in  which  oxygen  does  not  ex- 
ist ;  hence  its  property  of  preserving  potassium  which  has  so  strong 
an  affinity  for  oxygen  as  to  absorb  it  from  all  other  fluids.  It  howev- 
er loses  this  property  by  exposure  to  the  atmosphere,  probably  be- 
cause it  absorbs  a  small  quantity  of  air,  or  moisture.  It  is  again  re- 
stored by  distillation.  C, 


VEGfiTATIO'N. 


It  is  too  late  this  morning  to  enter  upon  the  history  of  vegeta- 
tion.    We  shall  reserve  this  subject,  therefore,  for  our  next  in- 
terview, when  I  expect  that  it  will  furnish  us  with  ample 
for  another  conversation. 


CONVERSATION  XXII. 

'HISTORY  OF  VEGETATION. 

Mrs.  B.  THE  VEGETABLE  KINGDOM  may  be  considered  as 
the  link  which  unites  the  mineral  and  animal  creation  into  one 
common  chain  of  beings  :  for  it  is  through  the  means  of  vegeta- 
tion alone  that  mineral  substances  are  introduced  into  the  ani- 
mal system,  since,  generally  speaking,  it  is  from  vegetables  that 
all  animals  ultimately-  derive  their  sustenance. 

Caroline.  I  do  not  understand  that ;  the  human  species  sub- 
sists as  much  on  animal  as  on  vegetable  food,  and  there  are 
some  carnivorous  animals  that  will  eat  only  animal  food. 

Mrs.  B.  That  is  true ;  but  you  do  not  consider  that  those 
that  live  on  animal  food,  derive  their  sustenance  equally,  though 
not  so  immediately,  from  vegetables.  The  meat  that  we  eat 
is  formed  from  the  herbs  of  the  field,  and  the  prey  of  can 
rous  aiiKnals  proceeds,  either  directly  or  indirectly,  from  the 
same  source.  It  is,  therefore,  through  this  channel  that  the 
simple  elements  become  a  part  of  the  animal  frame.  We  should 
in  vain  attempt  to  derive  nourishment  from  carbon,  hydrogen, 
and  oxygen,  either  in  their  separate  state,  or  combined  in  the 
mineral  kingdom ;  for  it  is  only  by  being  united  in  the  form  of 
vegetable  combination,  that  they  become  capable  of  conveying 
nourishment. 

Emily.  Vegetation,  then,  seems  to  be  the  method  which 
Nature  employs  to  prepare  the  food  of  animals  ? 

Mrs.  B.  That  is  certainly  its  principal  object.  The  vegeta- 
ble creation  does  not  exhibit  more  wisdom  in  that  admirable 
system  of  organisation,  by  which  it  is  enabled  to  answer  its 
'own  immediate  ends  of  preservation,  nutrition,  and  propagation^ 
than  in  its  grand'and  ultimate  object  of  forming  those  arrange- 
ments and  combinations  of  principles,  which  are  so  well  adapted 
for  the  nourishment  of  animals. 

Emily.  But  I  am  very  curious  to  know  whence  vegetables 
obtain  their  principles  which  form  their  immediate  materials? 

Mrs.  B.  This  is  a  point  on  which  we  are  yet  so  much  in  the 
dark,  that  I  cannot  hope  fully  to  satisfy  your  curiosity  ;  but 


VEGETATION. 

what  little  I  know  on  this  subject,  I  will  endeavour  to  explain 
to  you. 

The  soil,  which,  at  first  view,  appears  to  be  the  aliment  of 
vegetables,  is  found,  on  a  closer  investigation,  to  be  little  more 
than  the  channel  through  which  they  receive  their  nourish- 
ment ;  so  that  it  is  very  possible  to  rear  plants  without  any 
earth  or  soil.* 

*  The  opinion  that  water  is  the  only  food  of  plants,  was  adopted  by 
the  learned  on  this  subject  in  the  17th  century;  and  many  experi- 
ments were  made  which  seemed  to  prove  that  this  was  the  truth. 
Among  others  was  a  famous  one  by  Van  Helmout,  which  for  a  long 
time  was  supposed  to  have  established  the  point  beyond  all  doubt. 
He  planted  a  willow  which  weighed  five  pounds,;  in  an  earthern  vessel 
containing  200  Ibs  of  dried  earth.  This  vessel  was  sunk  into  the 
ground,  and  the  tree  was  watered.,  sometimes  with  distilled,  and  some- 
times with  rain  water. 

At  the  end  of  five  years  the  willow  weighed  169  Ibs  ;  and  on  weigh- 
ing the  soil,  dried  as  before,  it  was  found  to  have  lost  only  two  oun- 
ces. Thus  the  willow  had  gained  164  Ibs,  and  yet  its  food  had  been 
only  water.  The  induction  from  this  experiment  was  obvious.  Plants 
live  on  pure  water.  This  therefore  was  the  general  opinion,  uutill 
the  progress  of  chemistry  detected  its  fallacy.  Bergman,  in  1773 
showed  by  some  experiments  that  the  water,  which  Van  Helmout  had 
used  contained  as  much  earth  as  could  exist  in  the  tree  at  the  end  oi 
the  five  years ;  a  pound  of  water  containing  about  a  grain  of  earth, 
So  that  this  experiment  by  no  means  proved  that  the  willow  lived  on 
water  alone.  Since  this  time  a  great  variety  of  exp'-riments  have 
been  made  for  the  purpose  of  deciding  what  was  the  food  of  plants. 
la  the  course  of  these,  it  has  been  found,  that  although  seeds  do  vege- 
tat&in  pure  distilled  water,  yet  the  plant  is  weakly,  and  finally  dies 
before  the  fruit  is  matured. 

It  id  pretty  certain  then  that  earth  is  absolutely  necessary  to  the 
growth  of  plants,  and  that  a  part  of  their  food  is  taken  from  the  soil. 
Indeed,  the  well  known  fact  that  a  soil  is  worn  out  by  a  long  succes- 
sion of  crops,  and  finally  becomes  sterile,  unltss  manured,  is  good  proof 
that  plants  do  absorb  something  from  it. 

Saussure  has  shown  that  this  is  the  fact,  and  also  that  the  earth, 
which  is  always  found  in  plants,  is  of  the  same  kind,  as  that  on  which 
they  grow.  Thus  trees  growing  in  a  granitic  soil  contain  a  large  pro- 
portion of  silica,  while  those  growing  in  a  calcarious  soil,  contain  lit" 
tie  silica,  but  a  great  proportion  'of  calcareous  earth. 

In  addition  to  what  plants  absorb  from  the  ground,  there  is  no  doubt 
but  they  obtain  a  part  of  their  nourishment  fiom  water  and  air. 
Some  experiments  made  at  Berlin,  show  that  wheat,  barley,  &c.  con- 
tain a  quantity  of  earth,  though  fed  only  on  distilled  water. 

From  the  air  plants  absorb  carbonic  acid  gas.  The  carbon  they 
retain,  which  forms  the  greatest  part  of  their  bulk.  The  oxygen  is 
omitted,  and  goes  to  purify  the  atmosphere. 

Thus  it  is  seen  that  plants  obtain  their  food  from  the  earth,  from  wa- 
*er.  and  from  the  air  C. 


274  VEGETATiON. 

Caroline.  Of  that  we  have  an  instance  in  the  hyacinth,  and 
other  bulbous  roots,  which  will  grow  and  blossom  beautifully  in 
glasses  of  water.  But  I  confess  I  should  think  it  would  be  dif- 
ficult to  rear  trees  in  a  similar  manner. 

Mrs.  B.  No  doubt  it  would,  as  it  is  the  burying  of  the  roots 
in  the  earth  that  supports  the  stem  of  the  tree.  But  this  office, 
besides  that  of  affording  a  vehicle  for  food,  is  far  the  most  im- 
portant part  which  the  earthy  portion  of  the  soil  performs  in 
the  process  of  vegetation  ;  for  we  can  discover,  by  analysis, 
but  an  extremely  small  proportion  of  earth  in  vegetable  com- 
pounds. 

Caroline.  But  if  earths  do  not  afford  nourishment,  why  is  it 
necessary  to  be  so  attentive  to  the  preparation  of  the  soil  ? 

Mrs.  B.  In  order  to  impart  it  those  qualities  which  render  it 
a  proper  vehicle  for  the  food  of  the  plant.  Water  is  the  chief 
nourishment  of  vegetables  5  if,  therefore,  the  soil  be  too  sandy, 
it  will  not  retain  a  quantity  of  water  sufficient  to  supply  the 
roots  of  the  plants.  If,  on  the  contrary,  it  abound  too  much 
with  clay,  the  water  will  lodge  in  such  quantities  as  to  threaten 
a  decomposition  of  the  roots.  Calcareous  soils  are,  upon  the 
whole,  the  most  favourable  to  the  growth  of  plants  :  soils  are, 
therefore,  usually  improved  by  chalk,  which,  you  may  recol- 
lect, is  a  carbonat  of  lime.  Different  vegetables,  however,  re- 
quire different  kinds  of  soils.  Thus  rice  demands  a  moist  re- 
tentive soil ;  potatoes  a  soft  sandy  soil  ;  wheat  a  firm  and  rich 
soil.  Forest  trees  grow  better  in  fine  sand  than  in  a  stiff  clay  ; 
and  a  light  ferruginous  soil  is  best  suited  to  fruit-trees. 

Caroline.  But  pray  what  is  the  use  of  manuring  the  soil  ? 

Mrs.  B.  Manure  consists  of  all  kinds  of  substances,  whether 
of  vegetable  or  animal  origin,  which  have  undergone  the  putrid 
fermentation,  and  are  consequently  decomposed,  or  nearly  so, 
into  their  elementary  principles.  And  it  is  requisite  that  these 
vegetable  matters  should  be  in  a  state  of  decay,  or  approaching 
decotn  posit  ion.  The  addition  of  calcareous  earth,  in  the  state 
of  chalk  or  lime,  is  beneficial  to  such  soils,  as  it  accelerates  the 
dissolution  of  vegetable  bodies.  Now,  I  ask  you  what  is  the 
utility  of  supplying  the  soil  with  these  decomposed  substances? 

Caroline.  It  is,  I  suppose,  "in  order  to  furnish  vegetables 
with  the  principles  which  enter  their  composition.  For  ma- 
nures not  only  contain  carbon,  hydrogen,  and  oxygen, -but  by 
their  decomposition  supply  the  soil  with  these  principles  in  their 
elementary  form.* 

*  Rut  what  is  the  use  of  all  this,  if  "  water  is  the  chief  nourishment 
of  vegetables .-"'  C. 


VEGETATION.  27& 

Mrs.  B.  Undoubtedly;  and  it  ts  for  this  reason  that  the  fin- 
est crops  are  produced  in  fields  that  were  formerly  covered  with 
woods,  because  their- soil  is  composed  of  a  rich  mould,  a  kind  ot 
vegetable  earth  which  abounds  in  those  principles. 

Emily.  This  accounts  for  the  plentifulness  of  the  crops  pro- 
Juced  in  America,  where  the  country  was  but  a  few  years  since 
covered  with  wood. 

Caroline.  But  how  is  it  that  animal  substances  are  reckoned 
to  produce  the  best  manure?  Does  it  not  appear  much  more 
natural  that  the  decomposed  elements  of  vegetables  should  be 
the  most  appropriate  to  the  formation  of  new  vegetables? 

Mrs.  l>.  The  addition  of  a  much  greater  proportion  of  nitro- 
gen, which  constitutes  the  chief  difference  between  animal  and 
vegetable  matter,  renders  the  composition  of  the  former  more 
complicated,  and  consequently  more  favourable  to  decomposi- 
tion. The  use  of  animal  substances  is  chiefly  to  give  the  first 
impulse  tMhe  fermentation  of  the  vegetable  ingredients  that  en- 
ter into  the  composition  of  manures.  The  manure  of  a  farm- 
yard is  of  that  description ;  but  there  is  scarcely  any  substance 
susceptible  of  undergoing  tiie  putrid  fermentation  that  will  not 
make  good  manure.  The  heat  produced  by  the  fermentation 
of  manure  is  another  circumstance  which  is  extremely  favour- 
able to  vegetation;  yet  this  heat  would  be  too  great  if  the  ma- 
nure was  laid  on  the  ground  during  the  height  of  fermentation j 
it  is  used  in  this  state  only  for  hot-beds  to  produce  melons,  cu- 
cumbers, and  such  vegetables  as  require  a  very  high  tempera- 
ture. 

Caroline.  A  difficulty  has  just  occurred  to  me  which  I  do 
not  know  how  to  remove.  Since  all  organised  bodies  are,  in 
the  common  course  of  nature,  ultimately  reduced  to  their  ele- 
mentary state,  they  must  necessarily  in  that  state  enrich  the  soil? 
and  afford  food  for  vegetation.  How  is  it,  then,  that  agriculture, 
which  cannot  increase  the  quantity  of  those  elements  that  are 
required  to  manure  the  earth,  can  increase  its  produce  so  won- 
dei  fully  as  is  found  to  be  the  case  in  all  cultivated  countries  ? 

Mrs.  B.  It  is  by  suffering  none  of  these  decaying  bodies  to 
be  dissipated,  but  in  applying  them  duly  to  the  soil.  It  is  by  a 
judicious  preparation  of  the  soil,  which  consists  in  fitting  it  ei- 
ther for  the  general  purposes  of  vegetation,  or  for  that  of  the 
particular  seed  which  is  to  be  sown.  Thus,  if  the  soil  be  too 
wet,  it  may  be  drained  ;  if  too  loose  and  sandy,  it  may  be  ren- 
dered more  consistent  and  retentive  of  water  by  the  addition  of 
clay  or  loam  ;  it  may  be  enriched  by  chalk,  or  any  kind  of  cal- 
careous earth.  On  soils  thus  improved,  manures  will  act  with 
double  efficacy,  and  if  attention  be  paid  to  spread  them  on  the 


'i  VEGETATION. 

ground  at  a  proper  season  of  the  year,  to  mix  them  with  the  sew 
So  that  they  may  be  generally  diffused  through  it,  to  destroy 
the  weeds  which  might  appropriate  these  nutritive  principles  to 
their  own  use,  to  remove  the  stones  which  would  impede  the 
growth  of  the  plant,  &c.  we  may  obtain  a  produce  an  hundred 
fold  more  abundant  than  the  earth  would  spontaneously  supply. 
Emily.  We  have  a  very  striking  instance  of  this  in  the  scan- 
ty produce  of  uncultivated  commons,  compared  to  the  rich  crops 
of  meadows  which  are  occasionally  manured. 

Caroline.  But,  Mrs.  B.,  though  experience  daily  proves  the 
advantage  of  cultivation,  there  is  still  a  difficulty  which  I  can- 
not get  over.  A  certan  quantity  of  elementary  principles  exist 
in  nature,  which  it  is  not  in  the  power  of  man  either  to  augment 
or  diminish.  Of  these  principles  you  have  taught  us  that  both 
the  animal  and  vegetable  creation  are  composed.  Now  the 
more  of  them  is  taken  up  by  the  vegetable  kingdom,  the  less,  it 
would  seem,  will  remain  for  animals;  and,  therefore,  the  more 
populous  the  earth  becomes,  the  less  it  will  produce. 

Mrs.  B.  Your  reasoning  is  very  plausible ;  but  experience 
every  where  contradicts  the  inference  you  would  draw  from  it ; 
for  we  find  that  the  animal  and  vegetable  kingdoms,  instead  of 
thriving,  as  you  would  suppose,  at  each  other's  expense,  al- 
ways increase  and  multiply  together.  For  you  should  recollect 
tl*it  animals  can  derive  the  elements  of  which  they  are  formed 
only  through  the  medium  of  vegetables.  And  you  must  allow 
that  your  conclusion  would  be  valid  only  if  every  particle  of  the 
several  principles  that  could  possibly  be  spared  from  other  pur- 
poses were  employed  in  the  animal  and  vegetable  creations. 
Now  we  have  reason  to  believe  that  a  much  greater  proportion 
of  these  principles  than  is  required  for  such  pusposes  remains 
either  in  an  elementary  state,  or  engaged  in  a  less  useful  mode 
of  combination  in  the  mineral  kingdom.  Possessed  of  such  im- 
mense resources  as  the  atmosphere  and  the  waters  afford  IKS,  for 
oxygen,  hydrogen,  and  carbon,  so  far  from  being  in  danger  of 
working  up  all  our  simple  materials,  we  cannot  suppose  that  we 
shall  ever  bring  agriculture  to  such  a  degree  of  perfection  as  to 
require  the  whole  of  what  these  resources  could  supply. 

Nature,  however,  in  thus  furnishing  us  with  an  inexhaustible 
stock  of  raw  materials,  leaves  it  in  some  measure  to  tlie  ingenu- 
ity of  man  to  appropriate  them  to  its  own  purposes.  But  like 
a  kind  parent,  she  stimulates  him  to  exertion,  by  setting  the 
example  and  pointing  out  the  way.  For  it  is  on  the  operations 
of  nature  that  all  the  improvements  of  art  are  founded.  The 
art  of  agriculture  consists,  therefore,  in  discovering  the  readiest 
method  of  obtaining  the  several  principles,  either  from  their 


VEGETATION*  277 

»rand  sources,  air  and  water,  or  from  the  decomposition  of  or- 
ganised bodies;  and  in  appropriating  them  in  the  best  mannep 
to  the  purposes  of  vegetation. 

Emily.  But,  among  the  sources  of  nutritive  principles,  I  am 
surprised  th^tyou  do  not  mention  the  earth  itself,  as  it  contains 
abundance  of  coals,  which  are  chiefly  composed  of  carbon. 

Mrs.  B.  Though  coals  abound  in  carbon,  they  cannot,  on 
account  of  their  hardness  and  impermeable  texture,  be  imme- 
diately subservient  to  the  purposes  of  vegetation. 

Emily.  No  ;  but  by  their  combustion  carbonic  acid  is  pro- 
duced ;  and  this  entering  into  various  combinations  on  the  sur- 
face of  the  earth,  may,  perhaps,  assist  in  promoting  vegetation. 

Mrs.  B.  Probably  it  may  in  some  degree  5  but  at  any  rate 
the  quantity  of  nourishment  which  vegetables  derive  from  that 
source  can  be  but  very  trifling,  and  must  entirely  depend  on  lo- 
cal circumstances. 

Caroline.  Perhaps  the  smoky  atmosphere  of  London  is  the 
cause  of  vegetation  being  so  forward  and  so  rich  in  its  vicinity  ? 

Mrs.  B.  I  rather  believe  that  this  circumstance  proceeds 
from  the  very  ample  supply  of  manure,  assisted,  perhaps,  by 
the  warmth  and  shelter  which  the  town  affords.  Far  from  at- 
tributing any  good  to  the  smoky  atmosphere  of  London,  I  con- 
fess I  like  to  anticipate  the  time  when  we  shall  have  made  such 
progress  in  the  art  of  managing  combustion,  that  every  particle 
of  carbon  will  be  consumed,  and  the  smoke  destroyed  at  the 
moment  of  its  production.  We  may  then  expect  to  have  the 
satisfaction  of  seeing  the  atmosphere  of  London  as  clear  as  that 
of  the  country. — But  to  return  to  our  subject :  I  hope  that  you 
are  now  convinced  that  we  shall  not  easily  experience  a  defi- 
ciency of  nutritive  elements  to  fertilize  the  earth,  and  that,  pro- 
vided we  are  but  industrious  in  applying  them  to  the  best  ad- 
vantage by  improving  the  art  of  agriculture,  no  limits  can  be 
assigned  to  the  fruits  th*at  we  may  expect  to  reap  from  our  la- 
bours. 

Caroline.  Yes ;  I  am  perfectly  satisfied  in  that  respect,  and 
I  can  assure  you  that  I  feel  already  much  more  interested  in  the 
progress  and  improvement  of  agriculture. 

Emily.  I  have  frequently  thought  that  the  culture  of  the  land 
was  not  considered  as  a  concern  of  sufficient  importance.  Man. 
ufactures  always  take  the  lead  ;  and  health  and  innocence  a-e 
frequently  sacrificed  to  the  prospect  of  a  more  profitable  em- 
ployment. It  has  often  grieved  me  to  see  the  poor  manufartu* 
rers  crowded  together  in  close  rooms,  and  confined  for  the  wh«./e 
day  to  the  most  uniform  and  sedentary  employment,  instead  of 

25 


278 


VEGETATION. 


being  engaged  in  that  innocent  and  salutary  kind  of  labour, 
which  Nature  seems  to  have  assigned  to  man  for  the  immedi- 
ate acquirement  of  comfort,  and  for  the  preservation  of  his 
existence.  I  am  sure  that  you  agree  with  me  in  thinking  so, 

Mrs.  B.  I  am  entirely  of  your  opinion,  my  dear,  in  regard 
to  the  importance  of  agriculture;  but  as  the  conveniences  of 
life,  which  we  are  all  enjoying,  are  not  derived  merely  from  the 
soil,  1  am  far  from  wishing  to  depreciate  manufactures.  Be- 
sides, as  the  labour  of  one  man  is  sufficient  to  produce  food  for 
several,  those  whose  industry  is  not  required  in  tillage  must  do 
something  in  return  for  the  food  that  is  provided  for  them. 
They  exchange,  consequently,  the  accommodations  for  the 
necessaries  of  life.  Thus  the  carpenter  and  the  weaver  lodge 
and  clothe  the  peasant,  who  supplies  them  with  their  daily 
bread.  The  greater  stock  of  provisions,  therefore,  which  the 
husbandman  produces,  the  greater  is  the  quantity  of  accommo- 
dation which  the  artificer  prepares.  Such  are  the  happy  ef- 
fects 'which  naturally  result  from  civilized  society.  It  would 
be  wiser,  therefore,  to  endeavour  to  improve  the  situation  of 
those  who  are  engaged  in  manufactures,  than  to  indulge  in  vain 
declamations  on  the  hardships  to  which  they  are  too  frequently 
exposed. 

But  we  must  not  yet  take  our  leave  of  the  subject  of  agricul- 
ture ;  we  have  prepared  the  soil,  it  remains  for  us  now  to  sow 
the  seed.  In  this  operation  we  must  be  careful  not  to  bury  it 
too  deep  in  the  ground,  as  the  access  of  air  is  absolutely  neces- 
sary to  its  germination  ;  the  earth  must,  therefore,  lie  loose  and 
light  over  it,  in  order  that  the  air  may  penetrate.  Hence  the 
use  of  ploughing  and  digging,  harrowing  and  raking,  &c.  A 
certain  degree  of  heat  and  moisture,  such  as  usually  takes  place 
in  the  spring,  is.  likewise  necessary. 

Caroline.  One  would  imagine  you  were  going  to  describe 
the  decomposition  of  an  old  plant,  rather  than  the  formation  of 
a  new  one ;  for  you  have  enumerated  all  the  requisites  of  fer- 
mentation. 

Mrs.  B.  Do  you  forget,  my  dear,  that  the  young  plant  de- 
rives its  existence  from  the  destruction  of  the  seed,  and  that  it 
is  actually  by  the  saccharine  fermentation  that  the  latter  is  de- 
composed ? 

Caroline.  True  ;  I  wonder  that  I  did  not  recollect  that. 
The  temperature  and  moisture  required  for  the  germination  of 
the  seed  is  then  employed  in  producing  the  saccharine  fermen- 
tation within  it  ? 


VEGETATION.  279 

Mrs.  B.  Certainly.  But,  in  order  to  understand  the  nature 
of  germination,  you  should  be  acquainted  with  the  different 
parts  of  which  the  seed  is  composed.  The  external  covering 
or  envelope  contains,  beside  the  .gerrn  of  the  future  plant,  the 
substance  which  is  to  constitute  ks  first  nourishment ;  this  sub- 
stance, which  is  called  the  parenchyma,  consists  of  fecula,  mu- 
cilage, and  oil,  as  we  formerly  observed. 

The  seed  is  generally  divided  into  two  compartments,  called 
lobes  or  cotyledons,  as  is  exemplified  by  this  bean  (PLATE  XV. 
fig.  1.) — the  dark-coloured  kind  of  string  which  divides  the 
lobes  is  called  the  radicle,  as  it  forms  the  root  of  the  plant,  and 
it  is  from  a  contiguous  substance,  called  plumula,  which  is  in- 
closed within  the  lobes,  that  the  stem  arises.  The  figure  and 
size  of  the  seed  depend  very  much  upon  the  cotyledons  ;  these 
vary  in  number  in  different  seeds ;  some  have  only  one,  as 
wheat,  oats,  bailey,  and  all  the  grasses ;  some  have  three,  oth- 
ers six.  But  most  seeds,  as  for  instance,  all  the  varieties  of 
beans,  have  two  cotyledons.  When  the  seed  is  buried  in  the 
earth,  at  any  temperature  above  40  degrees,  it  imbibes  water, 
which  softens  and  swells  the  lobes ;  it  then  absorbs  oxygen, 
which  combines  with  some  of  its  carbon,  and  is  returned  in  the 
form  of  carbonic  acid.  This  loss  of  carbon  increases  the  com- 
parative proportion  of  hydrogen  and  oxygen  in  the  seed,  and 
excites  the  saccharine  fermentation,  by  which  the  parenchyma- 
tous  matter  is  converted  into  a  kind  of  sweet  emulsion.  In 
this  form  it  is  carried  into  the  radicle  by  vessels  appropriated 
to  that  purpose ;  and  in  the  mean  time,  the  fermentation  hav- 
ing caused  the  seed  to  burst,  the  cotyledons  are  rent  asunder, 
die  radicle  strikes  into  the  ground  and  becomes  the  root  of  the 
plant,  and  hence  the  fermented  liquid  is  conveyed  to  the  plu- 
mula,  whose  vessels  have  been  previously  distended  by  the  heat 
of  the  fermentation.  The  plumula  being  thus  swelled,  as  it 
vere,  by  the  emulative  fluid,  raises  itself  and  springs  up  to  the 
surface  of  the  earth,  bearing  with  it  the  cotyledons,  which,  as 
soon  as  they  come  in  contact  with  the  air,  spread  themselves, 
:tnd  are  transformed  into  leaves. — If  we  go  into  the  garden,  we 
shall  probably  find  some  seeds  in  the  state  which  I  have  de- 
scribed— 

Emily.  Here  are  some  lupines  that  are  just  making  their  ap- 
pearance above  ground. 

Mrs.  B.  We  shall  take  up  several  of  them  to  observe  their 
different  degrees  of  progress  in  vegetation.  Here  is  one  that 
has  but  recently  burst  its  envelope — do  you  see  the  little  radi- 
cle striking  downwards  ?  (PLATE  XV.  fig.  2.)  In  this  thfi 


280  VEGETATION. 

plumula  is  not  yet  visible.  But  here  is  another  in  a  greater 
state  of  forwardness — the  plumula,  or  stem,  has  risen  out  of  the 
ground,  and  the  cotyledons  are  converted  into  seeds  leaves. 
(PLATE  XV.  fig.  3.) 

Caroline.  These  leaves  are  very  thick  and  clumsy;  and  un- 
like the  other  leaves,  which  I  perceive  are  just  beginning  to  ap- 
pear, 

Mrs.  JBf.  It  is  because  they  retain  the  remains  of  the  paren- 
chyma, with  which  they  still  continue  to  nourish  the  young 
plant,  as  it  has  not  yet  sufficient  roots  and  strength  to  provide 
for  its  sustenance  from  the  soil. — But,  in  this  third  lupine 
(PLATE  XIV.  fig.  4.,)  the  radicle  had  sunk  deep  into  the  earth, 
and  sent  out  several  shoots,  each  of  which  is  furnished  with  a 
mouth  to  suck  up  nourishment  from  the  soil  5  the  function  of 
the  original  leaves,  therefore,  being  no  longer  required,  they 
are  gradually  decaying,  and  the  plumula  is  become  a  regular 
stem,  shooting  out  small  branches,  and  spreading  its  foliage. 

Emily.  There  seems  to  be  a  very  striking  analogy  between 
a  seed  and  an  egg  ;  both  require  an  elevation  of  temperature 
to  be  brought  to  life ;  both  at  first  supply  with  aliment  the  or- 
ganised being  which  they  produce;  and  as  soon  as  this  has  at- 
Cained  sufficient  strength  to  procure  its  own  nourishment,  the 
egg-shell  breaks,  whilst  in  the  plant  the  seed-leaves  fall  off. 

Mrs.  B.  There  is  certainly  some  resemblance  between  these 
processes ;  and  when  you  become  acquainted  with  animal  chem- 
istry, you  will  frequently  be  struck  with  its  analogy  to  that  of 
the  vegetable  kingdom. 

As  soon  as  the  young  plant  feeds  from  the  soil,  it  requires 
the  assistance  of  leaves,  which  are  the  organs  by  which  it 
throws  off  its  super-abundant  fluid ;  this  secretion  is  much  more 
plentiful  in  the  vegetable  than  in  the  animal  creation,  and  the 
great  extent  of  surface  of  the  foliage  of  plants  is  admirably  cal- 
culated for  carrying  it  on  in  sufficient  quantities.  This  trans- 
pired fluid  consists  of  little  more  than  water.  The  sap,  by  this 
process,  is  converted  into  a  liquid  of  greater  consistence, 
which  is  fit  to  be  assimilated  to  its  several  parts. 

Emily.  Vegetation,  then,  must  be  essentially  injured  by  de- 
stroying the  leaves  of  the  plant? 

Mrs.  B.  Undoubtedly;  it  not  only  diminishes  the  transpira- 
tion, but  also  the  absorption  by  the  roots;  for  the  quantity  of 
sap  absorbed  is  always  in  proportion  to  the  quantity  of  fluid 
thrown  off  by  transpiration.  You  see,  therefore,  the  necessity 
that  a  young  plant  should  unfold  its  leaves  as  soon  as  it  begins 
to  derive  its  nourishment  from  the  soil ;  and,  accordingly,  yon 


VEGETATION.  281 

will  And  that  those  lupines  which  have  dropped  their  seed- 
leaves,  and  are  no  longer  fed  by  the  parenchyma,  have  spread 
their  foliage,  in  order  to  perform  the  office  just  described. 

But  I  should  inform  you  that  this  function  of  transpiration 
seems  to  be  confined  to  the  upper  surface  of  the  leaves,  whilst, 
on  the  contrary,  the  lower  surface,  which  is  more  rough  and 
uneven,  and  furnished  with  a  kind  of  hair  or  down,  is  destined 
to  absorb  moisture,  or  such  other  ingredients  as  the  plant  de- 
rives from  the  atmosphere. 

As  soon  as  a  young  plant  makes  its  appearance  above  ground, 
light,  as  well  as  air,  becomes  necessary  to  its  preservation. 
Light  is  essential  to  the  developement  of  the  colours,  and  to 
the  thriving  of  the  plant.  You  may  have  often  observed  what 
a  predilection  vegetables  have  for  the  light.  If  you  wake  any 
plants  grow  in  a  room,  they  all  spread  their  leaves,  and  extend 
their  branches  towards  the  windows. 

Caroline.  And  many  plants  close  up  their  flowers  as  soon  as 
it  is  dark. 

Emily.  But  may  not  this  be  owing  to  the  cold  and  dampness 
of  the  evening  air  ? 

Mrs.  B.  That  does  not  appear  to  be  the  case ;  for  in  a 
course  of  curious  experiments,  made  by  Mr.  Senebier  of  Gene- 
va, on  plants  which  he  reared  by  lamp-light,  he  found  that  the 
flowers  closed  their  petals  whenever  the  lamps  were  extin- 
guished. 

Emily.  But  pray  why  is  air  essential  to  vegetation,  plants  do 
not  breathe  it  like  animals? 

Mrs.  B.  At  least  not  in  the  same  manner  ;  but  they  certain- 
ly derive  some  principles  from  the  atmosphere,  and  yield  others 
to  it.  Indeed  it  is  chiefly  owing  to  the  action  of  the  atmosphere 
and  the  vegetable  kingdom  on  each  other,  that  the  air  contin- 
ues always  fit  for  respiration,  But  you  will  understand  this 
better  when  I  have  explained  the  effect  of  water  on  plants. 

I  have  said  that  water  forms  the  chief  nourishment  of  plants ; 
it  is  the  basis  not  only  of  the  sap,  but  of  all  the  vegetable  juices. 
Water  is  the  vehicle  which  carries  into  the  plant  the  various 
salts  and  other  ingredients  required  for  the  formation  and  sup- 
port of  the  vegetable  system.  Nor  is  this  all;  part  of  the  wa- 
ter itself  is  decomposed  by  the  organs  of  the  plant ;  the  hydro- 
gen becomes  a  constituent  part  of  oil,  of  extract,  of  colouring 
matter,  &c.  whilst  a  portion  of  the  oxygen  enters  into  the  for- 
mation of  mucilage,  of  fecula,  of  sugar,  and  of  vegetable  acids. 
But  the  greater  part  of  the  oxygen,  proceeding  from  the  decom- 
position of  the  water,  is  converted  into  a  gaseous  state  by  the 

25* 


282  VEGETATION. 

caloric  disengaged  from  the  hydrogen  during  its  condensation 
in  the  formation  of  the  vegetable  materials.  In  this  state  the 
oxygen  is  transpired  by  the  leaves  of  plants  when  exposed  to 
the  sun's  rays.  Thus  you  find  that  the  decomposition  of  water, 
by  the  organs  of  the  plant,  is  not  only  a  means  of  supplying  it 
with  its  chief  ingredient,  hydrogen,  but  at  the  same  time  of  re- 
plenishing the  atmosphere  with  oxygen,  a  principle  which  re- 
quires continual  renovation,  to  make  up  for  the  great  consump- 
tion of  it  occasioned  by  the  numerous  oxygenations,  combus- 
tions, and  respirations,  that  are  constantly  taking  place  on  the 
surface  of  the  globe.* 

Emily.  What  a  striking  instance  of  the  harmony  of  nature. 

Mrs.  B.  And  how  admirable  the  design  of  Providence,  who 
makes  every  different  part  of  the  creation  thus  contribute  to  the 
support  and  renovation  of  each  other! 

But  the  intercourse  of  the  vegetable  and  animal  kingdoms 
through  the  medium  of  the  atmosphere  extends  still  further. 
Animals,  in  breathing,  not  only  consume  the  oxygen  of  the  air, 
but  load  it  with  carbonic  acid,  which,  if  accumulated  in  the  at- 
mosphere, would,  in  a  short  time,  render  it  totally  unfit  for  res- 
piration. Here  the  vegetable  kingdom  again  interferes  ;  it  at- 
tracts and  decomposes  the  carbonic  acid,  retains  the  carbon  for 
its  own  purposes,  and  returns  the  oxygen  for  ours.t 

Caroline.  How  interesting  this  is !  I  do  not  know  a  more 

*  The  foregoing  paragraph  might  mislead  the  student.  Indeed  it 
seems  to  have  been  written  without  regard  to  proper  authorities.  For 
instance,  there  is  no  proof  that  water  is  decomposed  by  the  organs  of 
plants  ;  nor  is  it  in  the  least  degree  probable  that  the  oxygen  emitted 
by  them  owes  its  gaseous  state,  to  the  caloric  set  free  by  the  condensa- 
tion of  hydrogen.  Authors  on  this  subject  agree  that  the  thickest  veil 
covers  the  processes  by  which  the  sap  is  converted  into  the  several 
parts  of  the  plant.  But  it  has  been  demonstrated,  that  most,  if  not  all 
the  oxygen  emitted  by  the  leaves,  is  obtained  by  the  decomposition  of 
air,  instead  of  water,  as  here  stated.  If  leaves  are  exposed  to  the  rays 
ef  the  sun,  while  under  commm  water,  they  emit  oxygen.  But  if  the 
water  is  first  deprived  of  its  air,  by  an  air  pump,  or  by  boiling,  not  » 
particle  of  oxygen  is  emitted.  Now  atmospheric  air,  always  contains 
a  quantity  of  carbonic  acid  gas,  and  experiments  show,  that  plants 
give  out  oxygen  in  some  proportion  to  the  quantity  of  this  gas  contain- 
ed in  the  waler.  The  fact  then  seems  to  be,  that  plants  absorb  car- 
bonic acid,  that  this  is  decomposed  by  some  unknown  process ;  the 
plant  retaining  the  carbon  while  the  oxygen  is  given  out.  C. 

t  It  is  a  curious  fact,  demonstrated  by  experiments,  that  the  leaves 
*f  plants  perform  different  offices  at  different  periods  of  the  24  hours. 
During  the  day  they  give  oat  water,  absorb  carbonic  acid,  and  emit 
oxygen  gas ;  but  during  the  night  they  absorb  water,  and  oxygen  gas. 
and  give  out  carbonic  acid.  C 


VEGETATION.  283 

beautiful  illustration  of  the  wisdom  which  is  displayed   in  the 
laws  of  nature. 

Mrs.  B.  Faint  and  imperfect  as  are  the  ideas  which  our  lim- 
ited perceptions  enable  us  to  form  of  divine  wisdom,  still  they 
cannot  fail  to  inspire  us  with  awe  and  admiration.  What, 
then,  would  be  our  feelings,  were  the  complete  system  of  nature 
at  once  displayed  before  us !  So  magnificent  a  scene  would 
probably  be  too  great  for  our  limited  and  imperfect  comprehen- 
sion, and  it  is  no  doubt  among  the  wise  dispensations  of  Provi- 
dence, to  veil  the  splendour  of  a  glory  with  which  we  should  be 
overpowered.  But  it  is  well  suited  to  the  nature  of  a  rational 
being  to  explore,  step  by  step,  the  works  of  the  creation,  to  en- 
deavour to  connect  them  into  harmonious  systems ;  and,  in  a 
word,  to  trace  in  the  chain  of  beings,  the  kindred  ties  and  be- 
nevolent design  which  unites  its  various  links,  and  secures  its 
preservation. 

Caroline.  But  of  what  nature  are  the  organs  of  plants  which 
are  endued  with  such  wonderful  powers? 

Mrs.  B.  They  are  so  minute  that  their  structure,  as  well  as. 
the  mode  in  which  they  perform  their  functions,  generally  elude 
our  examination  ;  but  we  may  consider  them  as  so  many  ves- 
sels or  apparatus  appropriated  to  perform,  with  the  assistance 
of  the  principle  of  life,  certain  chemical  processes,  by  means  of 
which  these  vegetable  compounds  are  generated.  We  may, 
however,  trace  the  tannin,  resins,  gum,  mucilage,  and  some  oth- 
er vegetable  materials,  in  the  organised  arrangement  of  plants, 
in  which  they  form  the  bark,  the  wood,  the  leaves,  flowers,  and 
seeds. 

The  bark  is  composed  of  the  epidermis,  the  parenchyma, 
and  the  cortical  layers. 

The  epidermis  is  the  external  covering  of  the  plant.  It  is  a 
thin  transparent  membrane,  consisting  of  a  number  of  slender 
fibres,  crossing  each  other,  and  forming  a  kind  of  net-work. 
When  of  a  white  glossy  nature,  as  in  several  species  of  trees,  in 
the  stems  of  corn  and  of  seeds,  it  is  composed  of  a  thin  coating 
of  siliceous  earth,  which  accounts  for  the  strength  and  hardness 
«f  those  long  and  slender  stems.  Sir  H.  Davy  was  led  to  the 
discovery  of  the  siliceous  nature  of  the  epidermis  of  such  plants, 
by  observing  the  singular  phenomenon  of  sparks  of  fire  emitted 
by  the  collision  of  ratan  canes  with  which  two  boys  were  fight- 
ing in  a  dark  room.  On  analysing  the  epidermis  of  the  cane? 
he  found  it  to  be  almost  entirely  siliceous.* 

*  In  the  scouring  rash,  (Equiselwn  hyemale)  the  siliceous  epider- 
mis is  still  jpaore  obvious.  If  drawn  across  a  piece  of  soft  metal,  a^ 


284  VEGETATION. 

Caroline.  With  iron  then,  a  cane,  I  suppose,  will  strike  fire 
very  easily  ? 

Mrs.  B.  I  understand  that  it  will. — In  ever-greens  the  epi- 
dermis is  mostly  resinous,  and  in  some  few  plants  is  formed  of 
wax.  The  re:»in,  from  its  want  of  affinity  for  water,  tends  to 
preserve  the  plant  from  the  destructive  effects  of  violent  rains, 
severe  climates,  or  inclement  seasons,  to  which  this  species  of 
vegetables  is  peculiarly  exposed. 

Emily.  Resin  must  preserve  wood  just  like  a  varnish,  as  it 
is  the  essential  ingredient  of  varnishes  ? 

Mrs.  B.  Yes;  and  by  this  means  it  prevents  likewise  all  un- 
necessary expenditure  of  moisture. 

The  parenchyma  is  immediately  beneath  the  epidermis ;  it 
is  that  green  rind  which  appears  when  you  strip  a  branch  of 
any  tree  or  shrub  of  its  external  coat  of  bark.  The  parenchy- 
ma is  not  confined  to  the  stem  or  branches,  but  extends  over 
every  part  of  the  plant.  It  forms  the  green  matter  of  the 
leaves,  and  is  composed  of  tubes  filled  with  a  peculiar  juice. 

The  cortical  layers  are  immediately  in  contact  with  the 
wood;  they  abound  with  tannin  and  gallic  acid,  and  consist  of 
small  vessels  through  which  the  sap  descends  after  being  elabo- 
rated in  the  leaves.  The  cortical  layers  are  annually  renewed, 
the  old  bark  being  converted  into  wood. 

Emily.   But  through  what  vessels  does  the  sap  ascend?' 

Mrs.  B.  That  function  is  performed  by  the  tubes  of  the  al- 
burnum, or  wood,  which  is  immediately  beneath  the  cortical 
layers.  The  wood  is  composed  of  woody  fibre,  mucilage,  and 
resin.  The  fibres  are  disposed  in  two  ways;  some  of  them 
longitudinally,  and  these  form  what  is  called  the  silver  grain  of 
the  wood.  The  others,  which  are  concentric,  are  called  the 
spurious  grain.  These  last  are  disposed  in  layers,  from  the 
number  of  which  the  age  of  the  tree  may  be  computed,  a  new 
one  being  produced  annually  by  the  conversion  of  the  bark  in- 
to wood.  The  oldest,  amh^onsequently  most  internal  part  of 
the  alburnum,  is  called  heart-wood ;  it  appears  to  be  dead,  at 
least  no  vital  functions  are  discernible  in  it.  It  is  through  the 
tubes  of  the  living  alburnum  that  the  sap  rises.  These,  there- 
fore, spread  into  the  leaves,  and  there  communicate  with  the 
extremities  of  the  vessels  of  the  cortical  layers,  into  which  they 
pour  their  contents. 

Caroline.  Of  what  use,  then,  are  the  tubes  of  the  parenchy- 

silver  or  copper,  i*  ij^uts  it  likfc  a  file     It  even  makes  an  impression  oh 
the  hardest  steeL    C-. 


VEGETATION.  %W 

ina,  since  neither  the  ascending  nor  descending  sap  passes 
through  them  ? 

Mrs.  B.  They  are  supposed  to  perform  the  important  func- 
tion of  secreting  from  the  sap  the  peculiar  juices  from  which  the 
plant  more  immediately  derives  its  nourishment.  These  juic- 
es are  very  conspicuous,  as  the  vessels  which  contain  them  are 
much  larger  than  those  through  which  the  sap  circulates.  The 
peculiar  juices  of  plants  differ  much  in  their  nature,  not  only  in 
different  species  of  vegetables,  but  frequently  in  different  parts 
of  the  same  individual  plant :  they  are  sometimes  saccharine, 
as  in  the  sugar-cane,  sometimes  resinous,  as  in  firs  and  ever- 
greens, sometimes  of  a  milky  appearance,  as  in  the  laurel. 

Emily.  I  have  often  observed,  that  in  breaking  a  young 
shoot,  or  in  bruising  a  leaf  of  laurel,  a  milky  juice  will  ooze  out 
in  great  abundance. 

Mrs.  B.  And  it  is  by  making  incisions  in  the  bark  that  pitch, 
tar,  and  turpentine*  are  obtained  from  fir-trees.  The  durabili- 
ty of  this  species  of  woed  is  chiefly  owing  to  the  resinous  nature 
of  its  peculiar  juices.  The  volatile  oils  have,  in  a  great  meas- 
ure the  same  preservative  effects,  as  they  defend  the  parts,  with 
which  they  are  connected,  from  the  attack  of  insects.  This 
tribe  seems  to  have  as  great  an  aversion  to  perfumes,  as  the 
human  species  have  delight  in  them.  They  scarcely  ever  at- 
tack any  odoriferous  parts  of  plants,  and  it  is  not  uncommon 
to  see  every  leaf  of  a  tree  destroyed  by  a  blight,  whilst  the  blos- 
soms remain  untouched.  Cedar,  sandal,  and  all  aromatic 
woods,  are  on  this  account  of  great  durability. 

Emily.  But  the  wood  of  the  oak,  which  is  so  much  esteem- 
ed for  its  durability,  has,  I  believe,  no  smell.  Does  it  derive 
this  quality  from  its  hardness  alone  ? 

Airs.  B.  Not  entirely ;  for  the  chesnut,  though  considerably 
harder  and  firmer  than  the  oak,  is  not  so  lasting.  The  dura- 
bility of  the  oak  is,  I  believe,  rn  a  great  measure  owing  to  its 
having  very  little  heart-wood,  the  alburnum  preserving  its  vital 
functions  longer  than  in  other  trees. 

Caroline.  If  incisions  are  made  into  the  alburnum  and  cor- 

*  Turpentine  is  obtained  as  described  in  the  te&t.  But  tar  and 
pitch  are  obtained  by  a  very  different  method.  A  conical  cavity  is 
dug  in  the  earth,  at  the  bottom  d  which  is  placed  a  reservoir.  Over 
this  is  piled  billets  of  fir- wood,  forming  a  large  pile.  The  pile  is  cov- 
ered with  turf  to  smother  the  fire,  which  is  kindled  at  the  top.  As  the 
wood  is  heated,  and  gradually  converted  into  charcoal,  the  tar  is  dri- 
ven out,  and  runs  into  the  cavity,  and  finally  into  the  reservoir.  Tar 
is  a  mixture  of  resin,  empyreumatis  oil,  charcoal,  and  acetic  acid. 
The  colour  is  derived  from  the  charcoal.  Pitch  is  made  by  boiling 
tar,  b^  which  Its  more  volatile  parts  are  driven  off.  C. 


VEGETATION. 


deal  layers,  may  not  the  ascending  and  descending  sap  be  pro- 
cured in  the  same  manner  as  the  peculiar  juice  is  from  the  ves- 
sels of  the  parenchyma  ? 

Mrs.  B.  Yes;  but  in  order  to  obtain  specimens  of  these  flu- 
ids, in  any  quantity,  the  experiment  must  be  made  in  the  spring, 
when  the  sap  circulates  with  the  greatest  energy.  For  this 
purpose  a  small  bent  glass  tube  should  be  introduced  into  the 
incision,  through  which  the  sap  may  flow  without  mixing  with 
any  of  the  other  juices  of  the  tree.  From  the  bark  the  sap 
will  flow  much  more  plentifully  than  from  the  wood,  as  the  as- 
cending sap  is  much  more  liquid,  more  abundant,  and  more  rap- 
id in  its  motion  than  that  which  descends  ;  for  the  latter  having 
been  deprived  by  the  operation  of  the  leaves  of  a  considerable 
part  of  its  moisture,  contains  a  much  greater  proportion  of  sol- 
id matter,  which  retards  its  motion.  It  does  not  appear  that 
there  is  any  excess  of  descending  sap,  as  none  ever  exudes  from 
the  roots  of  plants  ;  this  process,  therefore,  seems  to  be  carri- 
ed on  only  in  proportion  to  the  wants  of  the  plant,  and  the  sap 
descends  no  further,  and  in  no  greater  quantity,  than  is  requi- 
red to  nourish  the  several  organs.  Therefore,  though  the  sap 
rises  and  descends  in  the  plant,  it  does  not  appear  to  undergo  a 
real  circulation. 

The  last  of  the  organs  of  plants  is  the  jtfcwer,  or  blossom, 
which  produces  thefruits  and  seed.  These  may  be  considered 
as  the  ultimate  purpose  of  nature  in  the  vegetable  creation. 
From  fruits  and  seeds  animals  derive  both  a  plentiful  source  of 
immediate  nourishment,  and  an  ample  provision  for  the  repro- 
duction of  the  same  means  of  subsistence. 

The  seed  which  forms  the  final  product  of  mature  plants,  we 
have  already  examined  as  constituting  the  first  rudiments  of  fu- 
ture vegetation. 

These  are  the  principal  organs  of  vegetation,  by  means  of 
which  the  several  chemical  processes  which  are  carried  on  du- 
ring the  life  of  the  plant  are  performed. 

Emily.  But  how  are  the  several  principles  which  enter  into 
the  composition  of  vegetables  so  combined  by  the  organs  of  the 
plant  as  to  be  converted  into  vegetable  matter  ? 

Mrs.  B.  By  chemical  processes,  no  doubt  ;  but  the  appara- 
tus in  which  they  are  performed  is  so  extremely  minute  as  to 
elude  our  examination.  We  can  form  an  opinion,  therefore, 
only  by  the  result  of  these  operations.  The  sap  is  evidently 
composed  of  water,  absorbed  by  the  roots,  and  holding  in  so- 
lution the  various  principles  which  it  derives  from  the  soil. 
From  the  roots  the  sap  ascends  through  the  tubes  of  the  albur- 
num into  the  stem,  and  thence  branches  out  to  every  extremity 


VEGETATION.  287 

of  the  plant.  Together  with  the  sap  circulates  a  certain  quan- 
tity of  carbonic  acui,  which  is  gradually  disengaged  from  the 
former  hy  the  internal  heat  of  the  plant. 

Caroline.  What  ?  have  vegetables  a  peculiar  heat,  analo- 
gous to  animal  heat  ? 

Airs.  B.  It  is  a  circumstance  that  has  long  been  suspected ; 
but  late  experiments  have  decided  beyond  a  doubt,  that  vegeta- 
ble heat  is  considerably  above  that  of  unorganised  matter  in 
winter,  and  below  it  in  summer.  The  wood  of  a  tree  is  about 
sixty  degrees,  when  the  thermometer  is  seventy  or  eighty  de- 
grees. And  the  bark,  though  so  much  exposed,  is  seldom  be- 
low forty  in  winter. 

It  is  from  the  sap,  after  it  has  been  elaborated  by  the  leaves, 
that  vegetables  derive  their  nourishment  ;  in  its  progress 
through  the  plant  from  the  leaves  to  the  roots,  it  deposits  in  the 
several  sets  of  vessels  with  which  it  communicates,  the  materi- 
als on  which  the  growth  and  nourishment  of  each  plant  de- 
pends. It  is  thus  that  the  various  peculiar  juices,  saccharine, 
oily,  mucous,  acid,  and  colouring,  are  formed  ;  as  also  the 
inoie  solid  parts,  fecula,  woody  fibre,  tannin,  resins,  concrete 
salts  :  in  a  word,  all  the  immediate  materials  of  vegetables,  as 
well  as  the  organised  parts  of  plants,  which  latter,  besides  the 
power  of  secreting  these  from  the  sap  for  the  general  purpose  of 
the  plant,  have  also  that  of  applying  them  to  their  own  partic- 
ular nourishment. 

Emily.  But  why  should  the  process  of  vegetation  take  place 
only  at  one  season  of  the  year,  whilst  a  total  inaction  prevails 
during  the  other  ? 

Airs.  B  Heat  is  such  an  important  chemical  agenr,  that  its 
effect,  as  such,  might  perhaps  alone  account  for  the  impulse 
which  the  spring  gives  to  vegetation.  But,  in  order  to  explain 
the  mechanism  of  that  operation,  it  has  been  supposed  that  the 
warmth  of  the  spring  dilates  the  vessels  of  plants,  and  produ- 
ces a  kind  of  vacuum,  into  which  the  sap  (which  had  remained 
in  a  state  of  inaction  in  the  trunk  during  the  winter)  rises;  this 
is  followed  by  the  ascent  of  the  sap  contained  in  the  roots,  and 
room  is  thus  made  for  fresh  sap,  which  the  roots,  in  their  turn, 
pump  up  from  the  soil.  This  process  goes  on  till  the  plant 
blossoms  and  bears  fruit,  which  terminates  its  summer  career : 
but  when  the  cold  weather  sets  in,  the  fibres  and  vessels  con- 
tract, the  leaves  wither,  and  are  no  longer  able  to  perform  their 
office  of  transpiration  ;  and  as  this  secretion  stops,  the  roots 
cease  to  absorb  sap  from  the  soil.  If  the  plant  be  an  annual, 
its  life  then  terminates ;  if  not,  it  remains  in  a  state  of  torpid 
inaction  during  the  winter;  or  the  only  .internal  motion  that 


288  COMPOSITION 

takes  place  is  that  of  a  small  quantity  of  resinous  juice,  which 
slowly  rises  from  the  stem  into  the  branches,  and  enlarges  their 
buds  during  the  winter. 

Caroline.    Yet,   in  evergreens,  vegetation   must   continue 
throughout  the  year. 

Mrs.  B.  Yes;  but  in  winter  it  goes  on  in  a  very  imperfect 
manner,  compared  to  the  vegetation  of  spring  and  summer. 

We  have  dwelt  much  longer  on  the  history  of  vegetable 
chemistry  than  I  had  intended;  but  we  have  at  length  I  think, 
brought  the  subject  to  a  conclusion. 

Caroline.  I  rather  wonder  that  you  did  not  reserve  the  ac- 
count of  the  fermentations  for  the  conclusion ;  for  the  decom- 
position of  vegetables  naturally  follows  their  death,  and  can 
hardly,  it  seems,  be  introduced  with  so  much  propriety  at  any 
other  period. 

J\lrs.  B.  It  is  difficult  to  determine  at  what  (point  precisely 
k  may  be  most  eligible  to  enter  on  the  history  of  vegetation ; 
every  part  of  the  subject  is  so  closely  connected,  and  forms 
such  an  uninterrupted  chain,  that  it  is  by  no  means  easy  to  di- 
vide it.  Had  I  begun  with  the  germination  of  the  seed,  which, 
at  first  view,  seems  to  be  the  most  proper  arrangement,  I  could 
not  have  explained  the  nature  and  fermentation  of  the  seed,  or 
have  described  the  changes  which  nvanure  must  undergo,  in  or- 
der to  yield  the  vegetable  elements.  To  understand  the  nature 
of  germination,  it  is  necessary,  I  think,  previously  to  decom- 
pose the  parent  plant,  in  order  to  become  acquainted  with  the 
materials  required  for  that  purpose.  I  hope,  therefore,  that, 
upon  second  consideration,  you  will  find  that  the  order  which  1 
have  adopted,  though  apparently  less  correct,  is  in  fact  the 
best  calculated  for  the  elucidation  of  the  subject. 


CONVERSATION  XXIII. 

ON  THE  COMPOSITION  OF  ANIMALS. 

Mrs.  B.  WE  are  now  come  to  the  last  branch  of  chemistry, 
which  comprehends  the  most  complicated  order  of  compound 
beings.  This  is  the  animal  creation,  the  history  of  which  can- 
not but  excite  the  highest  degree  of  curiosity  and  interest, 
though  we  often  fail  in  attempting  to  explain  the  laws  by  which 
it  is  governed. 

Emily.  But  since  all  animals  ultimately  derive  their  nour- 
ishment from  vegetables,  the  chemistry  of  this  order  of  beings 


OF    ANIMALS.  289 

must  consist  merely  in  the  conversion  of  vegetable  into  animal 
matter. 

Mrs.  B.  Very  true  ;  but  the  manner  in  which  this  is  effect- 
ed is,  in  a  great  measure,  concealed  from  our  observation.  This 
process  is  called  animalisation,  and  is  performed  by  peculiar 
organs.  The  difference  of  the  animal  and  vegetable  kingdoms 
does  not  however  depend  merely  on  a  different  arrangement  o/ 
combinations.  A  new  principle  abounds  in  the  animal  king- 
dom, which  is  but  rarely  and  in  very  small  quantities  found  in 
vegetables ;  this  is  nitrogen.  There  is  likewise  in  animal  sub- 
stances a  greater  and  more  constant  proportion  of  phosphoric 
acid,  and  other  saline  matters.  But  these  are  not  essential  to 
the  formation  of  animal  matter. 

Caroline.  Animal  compounds  contain,  then,  four  fundamen- 
tal principles  ;  oxygen,  hydrogen,  carbon,  and  nitrogen  ? 

Mrs.  B.  Yes  ;  and  these  form  the  immediate  materials  of  an- 
imals, which  are  gelatin^  albumen^  andj?6H«e.* 

Emily.  Are  those  all  ?  I  am  surprised  that  animals  should 
be  composed  of  fewer  kinds  of  materials  than  vegetables  ;  for 
they  appear  much  more  complicated  in  their  organisation. 

Mrs.  B.  Their  organisation  is  certainly  more  perfect  and  in- 
tricate, and  the  ingredients  that  occasionally  enter  into  their 
composition  are  more  numerous.  But  notwithstanding  the 
wonderful  variety  observable  in  the  texture  of  the  animal  or- 
gans, we  find  that  the  original  compounds,  from  which  all  the 
varieties  of  animal  matter  are  derived,  may  be  reduced  to  the 
three  heads  just  mentioned.  Animal  substances  being  the  most 
complicated  of  all  natural  compounds,  are  most  easily  suscept- 
ible of  decomposition,  RS  the  scale  of  attractions  increases  m 
proportion  to  the  number  of  constituent  principles.  Theii 
analysis  is,  however,  both  difficult  and  imperfect  ;  for  as  they 
cannot  be  examined  in  their  living  state,  and  are  liable  to  alter- 
ation immediately  after  .death,  it  is  probable  that,  when  submt- 
ted  to  the  investigation  of  a  chemist,  they  are  always  more  01 
less  altered  in  their  combinations  and  properties,  from  what  they 
were,  whilst  they  made  part  of  the  living  animal. 

Entity.  The  mere  diminution  of  temperature,  which  they  ex- 
perience by  the  privation  of  animal  heat,  must,  I  should  sup- 
pose, be  sufficient  to  derange  the  order  of  attractions  that  exist- 
ed during  life. 

*  These  are  the  principal  ingredients  oi  the  soft  parts.  But  in  ad- 
dition to  these,  animal  substances  contain,  c-dGiiri'ii.:'  matter  of  bluod, 
mucous,  sulphur,  phosphorus,  earths,  alkalies,  o<7s,  adds,  restw,  arid 
several  others,  -which  it  is  unnecessary  4o  specifv,  (; 

26 


29CT  COMPOSITION 

Mrs.  B.  That  fs  one  of  the  causes,  no  doubt  :  but  there  arc 
many  other  circumstances  which  prevent  us  from  studying  the 
nature  of  living  animal  substances.  We  must  therefore,  in  a 
considerable  degree,  confine  our  researches  to  the  phenomena 
of  these  compounds  in  their  inanimate  state. 

These  three  kinds  of  animal  matter,  gelatine,  albumen,  and 
iibrine,  form  the  basis  of  all  the  various  parts  of  the  animal 
system ;  either  solid,  as  the  skin,  flesh,  nerves,  membranes, 
cartilages,  and  bones  ;  or  fluid,  as  blood,  chyle,  milk,  mucus, 
the  gastric  and  pancreatic  juices,  bile, perspiration,  saliva, 
tears,  &c. 

Caroline.  Is  it  not  surprising  that  so  great  a  variety  of  sub- 
stances, and  so  different  in  their  nature,  should  yet  all  arise  from 
so  few  materials,  and  from  the  same  original  elements  ? 

Mrs.  B.  The  difference  in  the  nature  of  various  bodies  de- 
pends, as  I  have  often  observed  to  you,  rather  on  their  state  of 
combination,  than  on  the  materials  of  which  they  are  compo- 
sed. Thus,  in  considering  the  chemical  nature  of  the  creation 
in  a  general  point  of  view,  we  observe  that  it  is  throughout 
composed  of  a  very  small  number  of  elements.  But  when  we 
divide  it  into  the  three  kingdoms,  we  find  that,  in  the  mineral, 
the  combinations  seem  to  "result  from  the  union  of  elements 
casually  brought  together ;  whilst  in  the  vegetable  and  and  ani- 
mal kingdoms,  the  attractions  are  peculiarly  and  regularly  pro- 
duced by  appropriate  organs,  whose  action  depends  on  the  vi- 
tal principle.  And  we  may  further  observe,  that  by  means  ot 
certain  spontaneous  changes  and  decompositions,  the  elements 
of  one  kind  of  matter  become  subservient  to  the  reproduction 
of  another ;  so  that  the  three  kingdoms  are  intimately  connect- 
ed, and  constantly  contributing  to  the  preservation  of  each  oth- 
er. 

Emily.  There  is,  however,  one  very  considerable  class  of 
elements,  which  seems  to  be  confined  to  the  mineral  kingdom  : 
I  mean  metals. 

Mrs.  A.'.  Not  entirely ;  they  are  found,,  though  in  very  mi- 
nute quantities,  both  in  the  vegetable  and  animal  kingdoms.  A 
small  portion  of  earths  and  sulphur  enters  also  into  the  com- 
position of  organised  bodies.  Phosphorus,  however,  is  almost 
entirety  confined  to  the  animal  kingdom  ;  and  nitrogen,  bn* 
with  few  exceptions,  is  extremely  scarce  in  vegetables. 

Let  us  now  proceed  to  examine  the  nature  of  the  three  prin- 
cipal materials'  of  the  animal  system. 

Gelatine,  or  jelly,  is  the  chief  ingredient  of  skin,  and  of  all 
the  membranous  parts  oi ".animals.  It  may  be  obtained  from 


?JF    ANIMALS. 

these  substances,  by  means  of  boiling  water  under  the  forms  of 
^iue,  size,  isinglass,  and  transparent  jelly. 

Caroline.  Bu{  these  are  of  a  very  different  nature  ;  they  can- 
not therefore  be  all  pure  gelatine. 

Mrs.  B.  Not  entirely,  but  y^ery  nearly  so.  Glue*  is  extract- 
id  from  the  skin  of  animals.  Size  is  obtained  either  from  skin 
in  its  natural  state,  or  from  leather.  Isinglass  is  gelatine  pro- 
cured from  a  particular  species  of  fish;  it  is,  you  know,  of  this 
substance  that  the  finest  jelly  is  made,  and  this  is  done  by 
merely  dissolving  the  isinglass  in  boiling  water,  and  allowing 
the  solution  to  congeal. 

Emily.  The  wine,  lemon,  and  spices,  are,  I  suppose,  added 
only  to  flavour  the  jelly  ? 

Mrs.  B.  Exactly  so. 

Caroline.  But  jelly  is  often  made  of  hartshorn  shavings,  and 
of  calves'  feet;  do  these  substances  contain  gelatine  ? 

Mrs.  B.  Yes.  Gelatine  may  be  obtained  from  almost  any 
animal  substance, as  it  enters  more  or  less  into  the  composition 
of  all  of  them.  The  process  for  obtaining  it  is  extremely  sim- 
ple, as  it  consists  merely  in  boiling  the  substance  which  con- 
tains it,  with  water.  The  gelatine  dissolves  in  water,  and  may 
be  attained  of  any  degree  of  consistence  or  strength,  by  evapo- 
rating this  solution.  Bones  in  particular  produce  it  very  plen- 
tifully, as  they  consist  of  phosphat  of  lime  combined  or  cement- 
ed by  gelatine.  Horns,  which  are  a  species  of  bone,  will  yield 
abundance  of  gelatine.  The  horns  of  the  hart  are  reckoned  to 
produce  gelatine  of  the  finest  quality  ;  they  are  reduced  to  the 
state  of  shavings  in  order  that  the  jelly  may  be  more  easily  ex- 
tracted by  the  water.  It  is  of  hartshorn  shavings  that  the  jel- 
lies for  invalids  are  usually  made,  as  they  are  of  very  easy  di- 
gestion. 

Caroline,  ft  appears  singular  that  hartshorn,  which  yields 
such  a  powerful  ingredient  as  ammonia,  should  at  the  same  time 
produce  so  mild  and  insipid  a  substance  as  jelly  ? 

.Mrs.  B.  And  (what  is  more  surprising)  it  is  from  the  gela- 
tine of  bones  that  ammonia  is  produced.  You  must  observe, 
however,  that  the  processes  by  which  these  two  substances  are 
obtained  from  bones  are  very  different.  By  the  simple  action 
of  water  and  heat,  the  gelatine  is  separated ;  but  in  order  to 
procure  the  ammonia,  or  what  is  commonly  called  hartshorn, 
the  bones  must  be  distilled,  by  which  means  the  gelatine  is  de- 

*  Bones,  muscles,  tendons,  ligaments,  membranes,  and  skins,  all  of 
them  yield  glue.  But  the  best  is  made  irom  the  skins  of  oh!  animals. 

G.     \ 


292  COMPOSITION 

composed^  and  hydrogen  and  nitrogen  combined  in  the  form  o 
ammonia.     So  that  the  first  operation  is  a  mere  separation  OF 
ingredients,  whilst  the  second  requires  a  chemical  decomposi- 
tion. 

Caroline.  But  when  jelly  is  made  from  hartshorn  shavings, 
what  becomes  of  the  phosphat  of  lime  which  constitutes  the 
other  part  of  bones  ? 

Mrs.  B.  It  is  easily  separated  by  straining.  But  the  jelly  is 
afterwards  more  perfectly  purified,  and  rendered  transparent, 
by  adding  white  of  egg,  which  being  coagulated  by  heat,  rises 
to  the  surface  along  with  any  impurities. 

Emily.  I  wonder  that  bones  are  not  used  by  the  common 
people  to  make  jelly  ;  a  great  deal  of  wholesome  nourishment, 
might,  I  should  suppose,  be  procured  from  them,  though  the 
jelly  would  perhaps  not  be  quite  so  good  as  if  made  from  harts- 
horn shavings  ? 

Mrs.  B.  There  is  a  prejudice  among  the  poor  against  a  spe- 
cies.of  food  that  is  usually  thrown  to  the  dogs  ;  and  as  we  can- 
not expect  them  to  enter  into  chemical  considerations,  it  is  in 
some  degree  excusable.  Besides  it  requires  a  prodigious  quan- 
tity of  fuel  to  dissolve  bones  and  obtain  the  gelatine  from  them. 

The  solution  of  bones  in  water  is  greatly  promoted  by  an  ac- 
cumulation of  heat.  This  may  be  effected  by  means  of  an  ex- 
tremely strong  metallic  vessel,,  called  Papui's  digester,  in 
which  the  bones  and  water  are  enclosed,  without  any  possibili- 
ty of  the  steam  making  its  escape.  A  heat  can  thus  be  applied 
much  superior  to  that  of  boiling  water ;  and  bones,  by  this 
means,  are  completely  reduced  to  a  pulp.  But  the  process  still 
consumes  too  much  fuel  to  be  generally  adopted  among  the  low- 
er classes. 

Caroline.  And  why  should  not  a  manufacture  be  established 
for  grinding  or  macerating  bones,  or  at  least  for  reducing  them 
to  the  state  of  shavings,  when  I  suppose  they  would  dissolve  as 
readily  as  hartshorn  shavings? 

Mrs.  B.  They  could  not  be  collected  clean  for  such  a  pur- 
pose, but'they  are  not  lost,  as  they  are  used  for  making  harts- 
horn and  sal  ammoniac;  and.  such  is  the  superior  science  and 
industry  of  this  country,  that  we  now  send  sal  ammoniac  to  the 
Levant,  though  it  originally  came  to  us  from  Egypt. 

Emily.  When  jelly  is  made  of  isinglass,  does  it  leave  no  se- 
diment ? 

Mrs.  B.  No ;  nor  does  it  so  much  require  clarifying,  as  it 
consists  almost  entirely  of  pure  gelatine,  and  any  foreign  matter 
that  is  mixed  with  it,  is  thrown  off  during  the  boiling  in  UK 
form  of  scum. — These  are  processes  which  you  may  see  per 


OP    ANIMALS.  293 

formed  in  great  perfection  in  the  culinary  laboratory,  by  that 
very  able  and  most  useful  chemist  the  cook. 

Caroline.  To  what  an  immense  variety' of  purposes  chemis- 
try is  subservient ! 

Emily.  It  appears,  in  that  respect,  to  have  an  advantage  over 
most  other  arts  and  sciences  ;  for  these,  very  often,  have  a  ten- 
dency to  confine  the  imagination  to  their  own  particular  object, 
whilst  the  pursuit  of  chemistry  is  so  extensive  and  diversified, 
that  it  inspires  a  general  curiosity,  and  a  desire  of  enquiring  in- 
to the  nature  of  every  object. 

Caroline.  I  suppose  that  soup  is  likewise  composed  of  gela- 
tine ;  for,  when  cold,  it  often  assumes  the  consistence  of  jelly  ? 

Mrs.  B.  Not  entirely  ;  for  though  soups  generally  contain  a 
quantity  of  gelatine>  the  most  essential  ingredient  is  a  mucous 
or  extractive  matter,  a  peculiar  animal  substance,  very  soluble 
in  water,  which  has  a  sfrong  taste,  and  is  more  nourishing  than 
gelatine.  The  various  kinds  of  portable  soup  consist  of  this  ex- 
tractive matter  in  a  dry  state,  which,  in  order  to  be  made  into 
soup,  requires  only  to  be  dissolved  in  water. 

Gelatine,  in  its  solid"  state,  is  a  semiductile  transparent  sub- 
stance, without  either  taste  or  smell. — When  exposed  to  heat, 
in  contact  with  air  and  water,  it  first  swells,  then  fuses,  and 
finally  burns.  You  may  have  seen  the  first  part  of  this  opera- 
tion performed  in  the  carpenter's  glue  pot. 

Caroline.  But  you  said  that  gelatine  had  no  smell,  and  glue 
has  a  very  disagreeable  one. 

Mrs.  B.  Glue  is  not. pure  gelatine  ;  as  it  is  not  designed  for 
eating,  it  is  prepared  without  attending  to  the  state  of  the  ingre- 
dients, which  are  more  or  less  contaminated  by  particles  that 
have  become  putrid. 

Gelatine  may  be  precipitated  from  its  solution  in  water  by 
alcohol — We  shall  try  this  experiment  with  a  glass  of  warm 
jelly. — You  see  that  the  gelatine  subsides  by  the  union  of  the 
alcohol  and  the  water* 

Emily.  How  is  it,  then,  that  jelly  is  flavoured  with  wine, 
without  producing  any  precipitation  ? 

Mrs.  B.  Because  the  alcohol  contained  in  wine  is  already 
combined  with  water,  and  other  ingredients,  and  is  therefore 
not  at  liberty  to  act  upon  the  jelly  as  when  in  its  separate  state. 
Gelatine  is -soluble  both  in  acids  and  in  alkalies;  the  former, 
you  know,  are  frequently  used  to  season  jellies. 

Caroline.  Among  the  combinations  of  gelatine  we  must  not 
forget  one  which  you  formerly  mentioned  ;  that  with  tannin,  to 
form  leather. 

Mrs.  B.  True ;  but  you  must  observe  that  leather  can  be 
26* 


294  COMPOSITION 

produced  only  by  gelatine  in  a  membranous  state;  for  though 
pure  gelatine  and  tannin  will  produce  a  substance  chemically 
similar  to  leather,  yet  the  texture  of  the  skin  is  requisite  to  make 
it  answer  the  useful  purposes  of  that  substance. 

The  next  animal  substance  we  are  to  examine  is  albumen  ,* 
this,  although  constituting  a  part  of  most  of  the  animal  com- 
pounds, is  frequently  found  insulated  in  the  animal  system  j 
the  white  of  egg,  for  instance,  consists  almost  entirely  of  albu- 
men ;  the  substance  that  composes  the  nerves,  the  serum,  or 
white  part  of  the  blood,  and  the  curds  of  milk,  are  little  else 
than  albumen  variously  modified. 

In  its  most  simple  state,  albumen  appears  in  the  form  of  a 
transparent  viscous  fluid,  possessed  of  no  distinct  taste  or  smell ; 
it  coagulates  at  the  low  temperature  of  165  degrees,  and,  when 
once  solidified,  it  will  never  return  to  its  fluid  state. 

Sulphuric  acid  and  alcohol  are  each  of  them  capable  of  coag- 
ulating albumen  in  the  same  manner  as  heat,  as  I  am  going  to 
show  you. 

Emily.  Exactly  so. — Pray,  Mrs.  B.,  what  kind  of  action  is 
there  between  albumen  and  silver  ?  I  have  sometimes  observ- 
ed, that  if  the  spoon  with  which  I  eat  an  egg  happens  to  be 
wetted,  it  becomes  tarnished. 

Mrs.  B.  It  is  because  the  white  of  egg  (and,  indeed,  albu- 
men in  general)  contains  a  little  sulphur,  which,  at  the  tempe- 
rature of  an  egg  just  boiled,  will  decompose  the  drop  of  water 
that  wets  the  spoon,  and  produce  sulphurated  hydrogen  gas? 
which  has  the  property  of  tarnishing  silver. 

We  may  now  proceed  tojibrine.  This  is  an  insipid  and  in- 
odorous substance,  having  somewhat  the  appearance  of  fine* 
white  threads  adhering  together  5  it  is  the  essential  constituent 
of  muscles  or  flesh,  in  which  it  is  mixed  witSi  and  softened  by 
gelatine.  It  is  insoluble  both  in  water  and  alcohol,  but  sulphu- 
ric acid  converts  it  into  a  substance  very  analogous  to  gelatine. 

These  are  the  essential  and  general  ingredients  of  animal 
matter;  but  there  are  other  substances,  which,  though  not  pe- 
culiar to  the  animal  system,  usually  enter  into  its  composition,, 
such  as  oils,  acids,  salts,  &c. 

Animal  oz7is  the  chief  constituent  of  fat;  it  is  contained  in 
abundance  in  the  cream  of  milk,  whence  it  is  obtained  in  the 
form  of  butter. 

Emily.  Is  animal  oil  the  same  in  its  composition  as  vegeta- 
ble oils? 

Mrs.  B.  Not  the  same,  but  very  analogous.  The  chief  dif- 
ference is  that  animal  oil  contains  nitrogen,  a  principle  which 


OF    ANIMALS.  ^95 

seldom  enters  into  the  composition  of  vegetable  oils,  and  never 
in  so  large  a  proportion. 

There  are  a  few  Animal  acids,  that  is  to  say,  acids  peculiar 
to  animal  matter,  from  which  they  are  almost  exclusively  ob- 
tained. 

The  animal  acids  have  triple  bases  of  hydrogen,  carbon,  and 
nitrogen.  Some  of  them  are  found  native  in  animal  matter; 
others  are  produced  during  its  decomposition. 

Those  that  we  find  ready  formed  are : 

The  bombic  acid,  which  is  obtained  from  silk-worms. 

the  formic  acid,  from  ants. 

The  latic  acid,  from  the  whey  of  milk. 

The  sebacic,  from  oil  or  fat. 

Those  produced  during  the  decomposition  of  a;.imal  sub- 
stances by  heat,  are  the  prussic  and  zoonic  acids.  This  last 
is  produced  by  the  roasting  of  meat,  and  gives  it  a  brisk  fla- 
vour. 

Caroline.  The  class  of  animal  acids  is  not  very  extensive? 

Mrs.  B.  No;  nor  are  they,  generally  speaking,  of  great  im- 
portance. The  prussic  acid*  is,  I  think,  the  only  one  suffi- 
ciently interesting  to  require  any  further  comment.  It  can  be 
formed  by  an  artificial  process  without  the  presence  of  any  ani- 
mal matter;  and  it  may  likewise  be  obtained  from  a  variety, of 
vegetables,  particularly  those  of  the  narcotic  kind,  such  as  pop- 
pies, laurel,  &c.  But  it  is  commonly  obtained  from  blood,  by 
strongly  heating  that  substance  with  caustic  potash ;  the  alkali 
attracts  the  acid  from  the  blood,  and  forms  with  it  uprussiat  of 
potash.  From  this  state  of  combination  the  prussic  acid  can 
be  obtained  pure  by  means  of  other  substances  which  have  the 
power  of  separating  it  from  the  alkali. 

'Emily.  But  if  this  acid  does  not  exist  ready  formed  in  bloed, 
how  can  the  alkali  attract  it  from  thence? 

*  Prussir.  acid  can  be  obtained  from  Piussian  blue  (prussiate  of 
iron)  by  the  following'  process.  Take  4  ounce?  ofprussian  blue,  pul- 
verize it  finely,  and  mix  with  it  2  1-2  ounces  of  red  oxide  of  mercury 
(red  precipitate  /)  boil  the  mixture  with  li*  ounces  of  water  in  a  glass 
vessel,  frequently  stiring  it  with  a  stick.  Filter  the  solution,  which  is 
a  prussiate  of  mercury,  and  is  formed  by  the  transfer  of  the  prussic 
acid,  from  the  iron  to  the  mercury.  Put  this  solution  into  a  retort,  and 
add  to  it  two  ounces  of  clean  iron  filings  and  six  drachms  of  sulphuric 
acid,  and  distil  off  two  and  a  half  ounces  of  prussic  acid.  This  pro- 
cess requires  a  good  apparatus,  and  ought  not  to  be  undertaken  by 
any  one  who  has  not  a  knowledge  of  practical  chemistry  The  fumes 
during  the  distilation  ought  carefully  to  be  avoided  as  poisonous. 
Prussic  acid  has  of  late  been  much  used  in  medicine,  as  a  remedy  in 
consumption,  hooping  cough.  &c.  C, 


296  COMPOSITION 

Mrs.  B,  It  is  the  tripple  basis  only  of  this  acid  that  exists  in 
the  blood)  and  this  is  developed  and  brought  to  the  state  of 
acid,  during  the  combustion.  The  acid  therefore  is  first  form- 
ed, and  it  afterwards  combines  with  the  potash. 

Emily.  Now  I  comprehend  it.  But  how  can  the  prussic 
acid  be  artificially  made? 

Mrs.  B.  By  passing  ammoniacal  gas  over  red-hot  charcoal ; 
and  hence  we  learn  that  the  constituents  of  this  acid  are  hydro- 
gen, nitrogen,  and  carbon.  The  two  first  are  derived  from  the 
volatile  alkali,  the  last  from  the  combustion  of  the  charcoal. 

Caroline.  But  this  does  not  accord  with  the  system  of  oxy- 
gen being  the  principle  of  acidity. 

Mrs.  B.  The  colouring  matter  of  prussian  blue  is  called  an 
acid,  because  it  unites  with  alkalies  and  metals,  and  not  from 
any  other  characteristic  properties  of  acids;  perhaps  the  name 
is  not  strictly  appropriate.  But  this  circu instance,  together 
with  some  others  of  the  same  kind,  has  induced  several  chem- 
ists to  think  that  oxygen  may  not  be  the  exclusive  generator  of 
acids.  Sir  II.  Davy,  I  have  already  informed  you,  was  led  by 
his  experiments  on  dry  acids  to  suspect  that  water  might  be  es- 
sential to  acidity.  And  it  is  the  opinion  of  some  chemists  that 
acidity  may  possibly  depend  rather  on  the  arrangement  than 
on  the  presence  of  any  particular  principles.  But  we  have  not 
yet  done  with  the  prussic  acid,^  It  has  a  strong  affinity  for 
metallic  oxyds,  and  precipitates  the  solutions  of  iron  in  acids 
of  a  blue  colour.  This  is  the  prussian  blue,  or  prussiat  of  iron, 
so  much  used  in  the  arts,  and  with  which  I  think  you  must  be 
acquainted. 

Emily.  Yes,  I  am  ;  it  is  much  used  in  painting,  both  in  oil 
and  in  water  colours  ;  but  it  rs  not  reckoned  a  permanent  oil- 
colour. 

Mrs.  B.  That  defect  arises,  I  believe,  in  general,  from  its  be- 
ing badly  prepared,  which  is  the  case  when  the  iron  is  not  so 
fully  oxydated  -as  to  form  a  red  oxyd.  For  a  solution  of  green 
oxyd  of  iron  (in  which  the  metal  is  more  slightly  oxydated,) 
makes  only  a  pale  green,  or  even  a  white  precipitate,  with 
prussiat  of  potash:  and  this  gradually  changes  to  blue  by  be- 
ing exposed  to  the  air,  as  I  can  immediately  show  you. 

Caroline.  It  already  begins  to  assume  a  pale  blue  colour. 
But  how  does  the  air  produce  this  change  ? 

Mrs.  B.  By  oxydating  the  iron  more  perfectly.  If  we  pour 
some  nitrous  acid  on  it,  the  prussian  blue  colour  will  be  imme- 
diately produced,  as  the  acid  will  yield  its  oxygen  to  the  pre- 
cipitate and  fully  saturate  it  with  this  principle,  as  you  shall  sex' 


OF    ANIMALS.  297 

Caroline.  It  is  very  cniious  to  see  a  colour  change  so  instan- 
taneously. 

Mrs.  B.  Hence  you  perceive  that  prussian  blue  cannot  be  a 
permanent  colour,  unless  prepared  with  red  oxyd  of  iron,  since 
by  exposure  to  the  atmosphere  it  gradually  darkens,  fand  in  a 
short  time  is  no  longer  in  harmony  with  the  other  colours  of  the 
painting. 

Caroline.  But  it  can  never  become  darker,  by  exposure  to 
the  atmosphere,  than  the  true  prussian  blue,  in  which  the  oxyd 
is  perfectly  saturated  ? 

Mrs.  B.  Certainly  not.  But  in  painting,  the  artist  not  reck- 
oning upon  partial  alterations  in  his  colours,  gives  his  blue  tints 
that  particular  shade  which  harmonises  with  the  rest  of  the  pic- 
ture. If,  afterwards,  those  tints  become  darker,  the  harmony 
of  the  colouring  must  necessarily  be  destroyed. 

Caroline.  Pray,  of  what  nature  is  the  paint  called  carmine  ? 

Mrs.  B.  It  is  an  animal  colour  prepared  from  cochineal,  an 
insect,  the  infusion  of  which  produces  a  very  beautiful  red.* 

Caroline.  Whilst  we  are  on  the  subject  of  colours,  I  should 
like  to  learn  what  ivory  black  is  ? 

Mrs.  B.  It  is  a  carbonaceous  substance  obtained  by  the  com- 
bustion of  ivory.  A  more  common  species  of  black  is  obtain- 
ed from  the  burning  of  bone. 

Caroline.  But  during  the  combustion  of  ivory  or  bone,  the 
carbon,  I  should  have  imagined,  must  be  converted  into  carbo- 
nic acid  gas,  instead  of  this  black  substance  ? 

Mrs.  B.  In  this,  as  in  most  combustions,  a  considerable  part 
of  the  carbon  is  simply  volatilised  by  the  heat,  and  again  ob- 
tained concrete  on  cooling.  This  colour,  therefore,  may  bo 
called  the  soot  produced  by  the  burning  of  ivory  or  bone. 


CONVERSATION  XXIV. 

ON  THE  ANIMAL,  ECONOMY. 

Mrs.  B.  WE  have  now  acquired  some  idea  of  the  various 
.materials  which  compose  the  animal  system  ;  but  if  you  are 
curious  to  know  in  what  manner  these  substances  are  formed 
by  the  animal  organs,  from  vegetable,  as  well  as  from  animal 
substances,  it  will  be  necessary  to  have  some  previous  know- 

•*'  Carmine  is  obtained  by  precipitating  the  colouring  matter  from 
t+n  infusion  of  <he  insect  by  means  of  a  solution  of  tin,  C, 


298  ON  THE  'ANIMAL  ECONOMY. 

ledge  of  the  nature  and  functions  of  these  organs,  without  which 
it  is  impossible  to  form  any  distinct  idea  of  the  process  of  ani- 
malisation  and  nutrition. 

Caroline.  I  do  not  exactly  understand  the  meaning  of  the 
word  animalisation  ? 

Mrs.  B.  Animalisation  is  the  process  by  which  the  food  is 
assimilated,  that  is  to  say,  converted  into  animal  matter  ;  and 
nutrition  is  that  by  which  the  food  thus  assimilated  is  render- 
ed subservient  to  the  purposes  of  nourishing  and  maintaining 
the  animal  system. 

Emily.  This,  I  am  sure,  must  be  the  most  interesting  of  all 
the  branches  of  chemistry  ! 

Caroline.  So  I  think  ;  particularly  as  I  expect  that  we  shall 
hear  something  of  the  nature  of  respiration,  and  of  the  circula- 
tion of  the  blood  ? 

Jllrs.  B.  These  functions  undoubtedly  occupy  a  most  impor- 
tant place  in  the  history  of  the  animal  economy. — But  I  must 
previously  give  you  a  very  short  account  of  the  principal  or- 
gans by  which  the  various  operations  of  the  animal  sy steurare 
performed.  These  are: 

The  Bonea, 
Muscles, 
Blood  vessels, 
Lympat/tic  vessels. 
Glands,  and 
Nerves. 

The  bones  are  the  most  solid  part  of  the  animal  frame,  and 
in  a  great  measure  determines  its  form  and  dimensions.  You 
recalled,  I  suppose,  what  are  the  ingredients  which  enter  into 
their  composition  ? 

Caroline.   Yes ;  phosphat  of  lime,  cemented  by  gelatine. 

Mrs.  n.  During  the  earliest  period  of  animal  life,  they  con- 
sist almost  entirely  of  gelatinous  membrane  having  the  form  of 
the  bones,  but  of  a  loose  sponzy  texture,  the  cells  or  cavities  of 
which  are  destined  to  be  filled  with  phosphat  of  lime  ;  it  is  the 
gradual  acquisition  of  this  salt  which  gives  to  the  bones  their 
subsequent  hardness  and  durability.  Infants  first  receive  it 
from  their  mother's  milk,  and  afterwards  derive  it  from  all  ani- 
mal and  from  most  vegetable  food,  especially  farinaceous  sub- 
stances, such  as  wheat-flour,  which  contain  it  in  sensible  quan- 
tities. A  portion  of  the  phosphat,  after  the  bones  of  the  infant 
have  been  sufficiently  expanded  and  solidified,  is  deposited  in 
the  teeth,  which  consist  at  first  only  of  a  gelatinous  membran^ 


ON  THE  ANIMAL  ECONOMY.  -99 

or  case,  fitted  for  the  reception  of  this  salt ;  and  which,  after 
acquiring  hardness  within  the  gum,  gradually  protrude  from  it. 

Caroline.  How  very  curious  this  is  ;  and  how  ingeniously 
nature  has  first  provided  for  the  solidification  of  such  bones  as 
are  immediately  wanted,  and  afterwards  for  the  formation  of 
the  teeth,  which  would  not  only  be  useless,  but  detrimental  in 
infancy ! 

Mrs.  B.  In  quadrupeds  the  phosphats  of  lime  is  deposited 
likewise  in  their  horns,  and  the  hair  or  wool  with  which  they 
are  generally  clothed. 

In  birds  it  serves  also  to  harden  the  beaks  and  the  quills  of 
their  feathers. 

When  animals  are  arrived  at  a  state  of  maturity,  and  their 
bones  have  acquired  a  sufficient  degree  of  solidity,  the  phosphat 
of  lime  which  is  taken  with  the  food  is  seldom  assimilated,  ex- 
cepting when  the  female  nourishes  her  young  5  it  is  then  all  se- 
creted into  the  milk,  as  a  provision  for  the  tender  benes  of  the 
nursling. 

Emily.  So  that  whatever  becomes  superfluous  to  one  being, 
is  immediately  wanted  by  another  $  and  the  child  acquires 
strength  precisely  by  the  species  of  nourishment  which  is  no 
longer  necessary  to  mother.  Nature  is,  indeed,  an  admirable 
economist ! 

Caroline.  Pray,  Mrs.  B.,  does  not  the  disease  in  the  bones 
of  children,  called  the  rickets,  proceed  from  a  deficiency  of 
phosphat  of  lime  ? 

Mrs.  B.  I  have  heard  that  this  disease  may  arise  from  two 
causes  5  it  is  sometimes  occasioned  by  the  growth  of  the  mus- 
cles being  too  rapid  in  proportion  to  that  of  the  bones.  In  this 
case  the  weight  of  the  flesh  is  greater  than  the  bones  can  sup- 
port, and  presses  on  them  so  as  to  produce  a  swelling  of  the 
joints,  which  is  the  great  indication  of  the  rickets.  The  other 
cause  of  this  disorder  is  supposed  to  be  an  imperfect  digestion 
and  assimilation  of  food,  attended  with  an  access  of  acid,  which 
counteracts  the  formation  of  phosphat  of  lime.  In  both  in- 
stances, therefore,  care  should  be  taken  to  alter  the  child's  diet, 
not  merely  by  increasing  the  quantity  of  aliment  containing 
phosphat  of  lime,  but  also  by  avoiding  all  food  that  is  apt  to 
turn  acid  on  the  stomach,  and  to  produce  indigestion.  But  the 
best  preservative  against  complaints  of  this  kind  is,  no  doubt, 
good  nursing  :  when  a  child  has  plenty  of  air  and  exercise,  the 
digestion  and  assimilation  will  be  properly  performed,  no  acid 
will  be  produced  to  interrupt  these  functions,  and  the  muscles 
and  bones  will  grow  together  in  just  proportions. 

Caroline.  I  have  often  heard  the  rickets  attributed  to  bad 


360  ON  THE  ANIMAL  ECONOMY. 

nursing,  but  I  never  could  have  guessed  what  connection  there 
was  between  exercise  and  the  formation  of  the  bones. 

Mrs.  B.  Exercise  is  generally  beneficial  to  all  the  animal 
functions.  If  man  is  destined  to  labour  for  his  subsistence,  the 
bread  which  he  earns  is  scarcely  more  essential  to  his  health 
and  preservation,  than  the  exertions  by  which  he  obtains  it. 
Those  whom  the  gifts  of  fortune  have  placed  above  the  necessi- 
ty of  bodily  labour,  are  compelled  to  take  exercise  in  some  mode 
or  other,  and  when  they  cannot  convert  it  into  an  amusement, 
they  must  submit  to  it  as  a  task,  or  their  health  will  soon  expe- 
rience the  effects  of  their  indolence. 

Emily.  That  will  never  be  my  case  :  for  exercise,  unless  it 
becomes  fatigue,  always  gives  me  pleasure  ;  and,  so  far  from 
being  a  task,  is  to  me  a  source  of  daily  enjoyment.  I  often 
think  what  a  blessing  it  is,  that  exercise,  which  is  so  conducive 
to  health,  should  be  so  delightful ;  whilst  fatigue,  which  is  rather 
hurtful,  instead  of  pleasure,  occasions  painful  sensations.  So 
that  fatigue,  no  doubt,  was  intended  to  moderate  our  bodily  ex- 
ertions, as  satiety  puts  a  limit  to  our  appetites. 

Mrs.  B.  Certainly. — But  let  us  not  deviate  too  far  from  our 
subject. — The  bones  are  connected  together  by  ligaments, 
which  consist  of  a  white  thick  flexible  substance,  adhering  to 
their  extremities,  so  far  as  to  secure  the  joints  firmly,  though 
without  impeding  their  motion.  And  the  joints  are  moreover 
covered  by  a  solid,  smooth,  elastic,  white  substance,  called 
cartilage,  the  use  of  which  is  to  allow,  by  its  smoothness  and 
elasticity,  the  bones  to  slid<;  easily  over  one  another,  so  that 
the  joints  may  perform  their  office  without  difficulty  or  detri- 
ment 

Over  the  bones  the  muscles  are  placed  j  }hey  consist  of  bun- 
dles of  fibres  which  terminate  in  a  kind  of  string,  or  ligament, 
by  which  they  are  fastened  to  the  bones.  The  muscles  are  the 
organs  of  motion  ;  by  their  power  of  dilatation  and  contrac- 
tion,, they  |5ut  into  action  the  bones,  which  act  as  levers,  in  all 
the  motions  of  the  body,  and  form  the  solid  support  of  its  va- 
rious parts.  The  muscles  are  of  various  degrees  of  strength  or 
consistence  in  different  species  of  animals.  The  mammiferous 
tribe,  or  those  that  suckle  their  young,  seem  in  this  respect  to 
occupy  an  intermediate  place  between  birds  and  cold-blooded 
animals,  such  as  reptiles  and  fishes. 

Emily.  The  different  degrees  of  firmness  and  solidity  in  the 
muscles  of  these  several  species  of  animals  proceed,  I  imagine, 
from  the  different  nature  of  the  food  on  which  they  subsist  ? 

Mrs.  B.  No  ;  that  is  not  supposed  to  be  the  case  :  for  the  hu- 
man species,  who  are  of  the  mammiferous  tribe,  live  on 


ON  THE  ANIMAL  ECONOMW  oOI 

more  substantial  food  than  birds,  and  yet  the  latter  exceed  them 
in  muscular  strength.  We  shall  hereafter  attempt  to  account 
for  this  difference  ;  but  let  us  now  proceed  in  the  examination 
of  the  animal  functions. 

The  next  class  of  organs  is  that  of  the  vessels  of  the  body, 
the  office  of  which  is  to  convey  the  various  fluids  throughout  the 
frame.  These  vessels  are  innumerable.  The  most  considera- 
ble of  them  are  those  through  which  the  blood  circulates,  which 
are  of  two  kinds  :  the  arteries,  which  convey  it  from  the  heart 
to  the  extremities  of  the  body,  and  the  veins,  which  bring  it 
back  into  the  heart. 

Besides  these,  there  are  a  numerous  set  of  small  transparent 
vessels,  destined  to  absorb  and  convey  different  fluids  into  the 
blood;  they-  arc  generally  called  the  absorbent  or  lymphatic 
vessels  :  but  it  is  to  a  portion  of  them  only  that  the  function  oX 
conveying  into  the  blood  the  fluid  called  lymph  is  assigned. 

Emily.  Pray  what  is  the  nature  of  that  fluid  ? 

'Mrs.  B.  The  nature  and  use  of  the  lymph  have,  I  believe, 
never  been  perfectly  ascertained;  but  it  is  supposed  to  consist 
of  matter  that  has  been  previously  animalised,  and  which,  after 
answering  the  purpose  for  which  it  was  intended,  must,  in  reg- 
ular rotation,  make  way  for  the  fresh  supplies  produced  by 
nourishment.  The  lymphatic  vessels  pump  up  this  fluid  from 
every  part  of  the  system,  and  convey  it  into  the  veins  to  be 
mixed  with  the  blood  which  runs  through  them,  and  which,  is 
commonly  called  venous  blood. 

Caroline.  But  does  it  not  again  enter  into  the  animal  system 
through  that  channel  ? 

Mrs.  B.  Not  entirely  ;  for  the  venous  blood  does  not  return 
into  the  circulation  until  it  has  undergone  a  peculiar  change,  in 
which  it  throws  off  whatever  is  become  useless. 

Another  set  of  absorbent  vessels  pump  up  the  chyle  from  the 
stomach  and  intestines,  and  convey  it,  after  many  circumvolu 
tions,  into  the  great  vein  near  the  heart.* 

Emily.  Pray  what  is  chyle  ? 

Mrs.  B.  It  is  the  substance  into  which  food  is  converted  by 
digestion. 

Caroline.  One  set  of  the  absorbent  vessels,  then,  is  employ- 
ed in  bringing  away  the  old  materials  which  are  no  longer  fit 

*  This  is  a  mistake.  The  chyle  is  conveyed  into  the  trunk  of  the 
absorbent  system,  called  by  anatomists  the  thoracic  duct.  This  runs 
in  a  serpentine  direction  along  the  internal  side  of  the  back  bone  up 
to  the  Kubclavian  rein,  which  lies  under  the  collarbone  Into  this 
vein  the  chyle  is  discharged  and  mixes  with  the  blood,  and  before  it 
reaches  the  heart  it  is  converted  into  blood  itself.  C, 

27 


302  ON  THE  ANIMAL  ECONOMY. 

for  use;  whilst  the  other  set  is  busy  in  conveying  into  the  blood 
the  new  materials  that  are  to  replace  them. 

Emily.  What  a  great  variety  of  ingredients  must  enter  into 
tbe  composition  of  the  blood  ? 

Mrs.  ti.  You  must  observe  that  there  is  also  a  great  variety 
of  substances  to  be  secreted  from  it.  We  may  compare  the 
blood  to  a  general  receptacle  or  storehouse  for  all  kinds  oi  com- 
modities, which  are  afterwards  fashioned,  arranged,  and  dispo- 
sed of  as  circumstancs  require. 

There  is  another  set  of  asorbent  vessels  in  females  which  is 
destined  to  secrete  milk  for  the  nourishment  of  the  young. 

Emily.  Pray  is  not  milk  very  analogous  in  its  composition 
to  blood  ;  for,  since  the  nursling  derives  its  nourishment  from 
that  source  only,  it  must  contain  every  principle  which  the  ani- 
mal system  requires  ? 

Mrs.  B.  Very  true.  Milk  is  found,  by  its  analysis,  to  con- 
tain the  principal  materials  of  animal  matter,  albumen,  oil,  and 
phospkat  of  lime  ;  so  that  the  suckling  has  but  little  trouble 
to  digest  and  assimilate  this  nourishment.  But  we  shall  exa- 
mine the  composition  of  milk  more  fully  afterwards. 

In  many  parts  of  the  body  numbeis  of  small  vessels  are  col- 
lected together  in  little  bundles  called  glands^  from  a  Latin 
word  meaning  acorn,  on  account  of  the  resemblance  which  some 
of  them  bear  in  shape  to  that  fruit.  The  function  of  the  glands 
is  to  secrete.,  or  separate  certain  matters  from  the  blood. 

The  secretions  are  not  only  mechanical,  but  chemical  sepa- 
rations from  the  blood  ;  for  the  substances  thus  formed,  though 
contained  in  the  blood,  are  not  ready  combined  in  that  fluid. 
The  secretions  are  of  two  kinds,  those  which  form  peculiar  an- 
imal fluids,  as  bile,  tears,  saliva,  &c. ;  and  those  which  pro- 
duce the  general  materials  of  the  animal  system,  for  tiie  pur- 
pose of  recruiting  and  nourishing  the  several  organs  of  tlu 
body ;  such  as  albumen,  gelatine,  and  fibrine ;  the  latter  may 
be  distinguished  by  the  name  of  nutritive  secretions. 

Caroline.  I  am  quite  astonished  to  hear  that  all  the  seen  - 
tions  should  be  derived  from  the  blood. 

Emily.  I  thought  that  the  bile  was  produced  by  the  liver  ': 

Mrs.  B.  So  it  is ;  but  the  liver  is  nothing  more  tlv.n  a  ven, 
large  gland,  \vhich  secretes  the  bile  from  the  blood. 

The  last  of  the  animal  organs  which  we  have  mentioned  are 
the  nerves  ;  these  are  the  vehicles  of  sensation,  every  other  part 
of  the  body  being,  of  itself,  totally  insensible, 

Caroline.  They  must  then  be  spread  through  every  part  of 
the  frame,  for  we  are  every  where  susceptible  of  feeling. 

Emily.  Excepting  the  nails  and  the  hair. 


ON  THE  ANIMAL  EGONOMV.  303 

Mrs.  .B.  And  those  are  almost  the  only  parts  in  which  nerves 
cannot  be  discovered.  The  common  source  of  all  the  nerves  is 
the  brain  ;  thence  they  decend,  some  of  them  through  different 
apertures  in  the  skull,  but  the  greatest  part  through  the  back 
bone,  and  extend  themselves  by  innumerable  ramifications 
throughout  the  whole  body.  They  spread  themselves  over  the 
muscles,  penetrate  the  glands,  wind  round  the  vascular  system, 
and  even  pierce  into  the  interior  of  the  bones.  It  is  most  pro- 
bably through  them  that  the  communication  is  carried  on  be- 
tween the  mind  and  the  other  parts  of  the  body;  but  in  what 
manner  they  are  acted  on  by  the  mind,  and  made  to  re-act  on 
the  body,  is  still  a  profound  secret.  Many  hypotheses  have 
been  formed  on  this  very  obscure  subject,  but  they  are  all  equaU 
ly  improbable,  and  it  would  be  useless  for  us  to  waste  our  time 
in  conjectures  on  an  enquiry,  which,  in  all  probability,  is  be- 
yoiad  the  reach  of  human  capacity. 

Caroline.  Cut  you  have  not  mentioned  those  particular 
nerves  that  form  the  senses  of  hearing,  seeing,  smelling,  and 
tasting  ? 

Airs.  B.  They  are  considered  as  being  of  the  same  nature  as 
those  which  are  dispersed  over  every  part  of  the  body,  and  con- 
stitute the  general  sense  of  feeling.  The  different  sensations 
which  they  produce  arise  from  their  peculiar  situation  and  con- 
nection with  the  several  organs  of  taste,  smell,  and  hearing. 

Emily.  But  these  senses  appear  totally  different  fiom  that  of 
i  eel  ing  ? 

Mrs.  B.  They  are  all  of  them  sensations,  but  variously  mod* 
ified  according  to  the  nature  of  the  different  organs  in  which 
the  nerves  are  situated.  For,  as  we  have  formerly  observed,  it 
is  by  contact  only  that  the  nerves  are  affected.  Thus  odorifer- 
ous particles  must  strike  upon  the  nerves  of  the  nose,  in  order 
to  excite  the  sense  of  smelling  ;  in  the  same  manner  that  taste 
is  produced  by  the  particular  substance  coming  in  contact  with 
the  nerves  of  the  tongue.  It  is  thus  also  that  the  sensation  of 
sound  is  produced  by  the  concussion  of  the  air  striking  against 
the  auditory  nerve ;  and  sight  is  the  effect  of  the  light  falling  ur> 
on  the  optic  nerve.  These  various  senses,  therefore,  are  ef- 
fected only  by  the  actual  contact  of  particles  of  matter,  in  the 
same  manner  as  that  of  feeling. 

The  different  organs  of  the  animal  body,  though  easily  sepa- 
rated and  perfectly  distinct,  are  loosely  connected  together  by 
a  kind  of  spongy  substance,  in  texture  somewhat  resembling 
net-work,  called  the  cellular  membrane  ;  and  the  whole  is  cov- 
ered by  the  skin. 

The..?&/»,  as  well  as  tlje  bark  of  vegetables,  is  formed  of 


304  ON  THE  ANIMAL  ECONOMY. 

three  coats.  The  external  one  is  called  the  cuticle  or  epider- 
mis; the  second,  which  is  called  the  mucous  membrane,  is  of  a 
thin  soft  texture,  and  consists  of  a  mucous  substance,  which  in 
negroes  is  black,  and  is  the  cause  of  their  skin  appearing  ot 
that  colour. 

Caroline.  Is  then  the  external  skin  of  negroes  white  like 
,ours  ? 

Mrs.  IB.  Yes  ;  but  as  the  cuticle  is  transparent,  as  well  as 
porous,  the  blackness  of  the  mucous  membrane  is  visible  through 
if.  The  extremities  of  the  nerves  are  spread  over  this  skin,  so 
that  the  sensation  of  feeling  is  transmitted  through  the  cuticle. 
The  internal  covering  of  the  muscles,  which  is  properly  the 
skin,  is  the  thickest,  the  toughest,  and  most  resisting  of  the 
whole  ;  it  is  this  membrane*  which  is  so  essential  in  the  arts,  by 
forming  leather  when  combined  with  tannin. 

The  skin  which  covers  the  animal  body,  as  well  as  those 
membranes  that  form  the  coats  of  the  vessels,  consists  almost 
exclusively  of  gelatine  5  and  is  capable  of  being  converted  into 
ijrlue,  size,  or  jelly. 

The  cavities  betwen  the  muscles  and  the  skin  are  usually  fil- 
led with  fat,  which  lodges  in  the  cells  of  the  membranous  net 
before  mentioned,  and  gives  to  the  external  form  (especially  in 
the  human  figure)  that  roundness,  smoothness,  and  softness,  so 
essential  to  beauty. 

Emily.  And  the  skin  itself  is,  I  think,  a  very  ornamental 
part  of  the  human  frame,  both  from  the  fineness  of  its  texture, 
and  the  variety  and  delicacy  of  its  tints. 

Mrs.  B.  This  variety  and  harmonious  gradation  of  colours, 
proceed,  not  so  much  from  the  skin  itself,  as  from  the  internal 
organs  which  transmit  their  several  colours  through  it,  these  be- 
ing only  softened  and  blended  by  the  colour  of  the  skin,  which 
is  uniformly  of  a  yellowish  white. 

Thus  modified,  the  darkness  of  the  veins  appears  of  a  pale 
blue  colour,  and  the  floridness  of  the  arteries  is  changed  to  a 
delicate  pink.  In  the  most  transparent  parts,  the  skin  exhibits 
the  bloom  of  the  rose,  whilst  where  it  is  more  opaque  its  own 
colour  predominates  ;  and  at  the  joints,  where  the  bones  are 
most  prominent,  their  whiteness  is  often  discernible.  In 
a  word,  every  part  of  the  human  frame  seems  to  contribute  to 
its  external  grace ;  and  this  not  merely  by  producing  a  pleas- 
ing variety  of  tints,  but  by  a  peculiar  kind  of  beauty  which  be- 
longs to  each  individual  part.  Thus  it  is  to  the  solidity  and  ar- 
rangement of  the  bones  that  the  human  figure  owes  the  grandeur 
of  its  stature,  and  its  firm  and  dignified  deportment.  The  mus- 
cles delineate  the  form,  and  stamp  it  with  energy  and  grace. 


ON  ANIMALISATION.  305 

and  the  soft  substance  which  is  spread  over  them  smooths  their 
nijitredness,  and  gives  to  the  contours  the  gentle  undulations  of 
the  line  of  beauty.  Every  organ  of  sense  is  a  peculiar  and  sep- 
arate ornament;  and  the  skin,  which  polishes  the  surface,  and 
gives  it  that  charm  of  colouring  so  inimitable  by  art,  finally  con- 
spires to  render  the  whole  the  fairest  work  of  the  creation. 

]>ut  now  that  we  have  seen  in  what  manner  the  animal  frame 
is  formed,  let  us  observe  how*it  provides  for  its  support,  and 
how  the  several  organs,  which  form  so  complete  a  whole,  are 
nourished  and  maintafned. 

This  will  lead  us  to  a  more  particular  explanation  of  the  in- 
ternal organs  :  here  we  shall  not  meet  with  so  much  apparent 
beaut}',  because  these  parts  were  not  intended  by  nature  to  be 
exhibited  to  view ;  but  the  beauty  of  design,  in  the  internal  or- 
ganisation of  the  animal  frame,  is,  if  possible,  stiil  mote  remark- 
able than  that  of  the  external  parts. 

We  shall  defer  this  subject  till  our  next  interview. 


CONVERSATION  XXV. 

ON  ANIMALISATION.  NUTRITION.  AND 
RESPIRATION. 

JV/Yf.  B.  WE  have  now  learnt  of  what  materials  the  animal 
system  is  composed,  and  have  formed  some  idea  of  the  nature 
of  its  organisation.  In  order  to  complete  the  subject,  it  re- 
mains for  us  to  examine  in  what  manner  it  is  nourished  and 
supported. 

Vegetables,  we  have  observed,  obtain  their  nourishment 
from  various  substances,  either  in  their  elementary  state,  or  in  a 
very  simple  state  of  combination  j  as  carbon,  water,  and  salts, 
which  they  pump  up  from  the  soil ;  and  carbonic  acid  and  ox- 
ygen, which  they  absorb  from  the  atmosphere. 

Animals,  on  the  contrary,  feed  on  substances  of  the  most 
complicated  kind  ;  for  they  derive  their  sustenance,  some  from 
the  animal  creation,  others  from  the  vegetable  kingdom,  and 
some  from  both. 

Caroline.  And  there  is  one  species  of  animals,  which,  not 
.satisfied  with  enjoying  either  kind  of  food  in  its  simple  state, 
has  invented  the  art  of  combining  them  together  in  a  thousand 
ways,  and  of  rendering  even  the  mineral  kingdom  % subservient 
to  its  refinements. 

Emily.  Nor  is  this  all ;.  for  our  delicacies  are  collected  from 
27* 


306  ON    NUTRITION. 

the  various  climates  of  the  earth,  so  that  the  four  quarters  of 
the  globe  are  often  obliged  to  contribute  to  the  preparation  of 
our  simplest  dishes. 

Caroline.  But  the  very  complicated  substances  which  con- 
stitute the  nourishment  of  animals,  do  not,  I  suppose,  enter  in- 
to their  system  in  their  actual  state  of  combination  ? 

Mrs.  B.  So  far  from  it,  that  they  not  only  undergo  a  new  ar- 
rangement of  their  parts,  but  a  selection  is  made  of  such  as  are 
most  proper  for  the  nourishment  of  the  body,  and  those  only 
enter  into  the  system,  and  are  animalised. 

Emily.  And  by  what  organs  is  this  process  performed  ? 

*t;rs.  ij.  Chiefly  by  the  stomach,  which  is  the  organ  of  di- 
gestion, and  the  prime  regulator  of  the  animal  frame. 

Digestion  is  the  first  step  toward  nutrition.  It  consists  in 
reducing  into  one  homogeneous  mass  the  various  substances 
that  are  taken  as  nourishment;  it  is  performed  by  first  chewing 
and  mixing  the  solid  aliment  with  the  saliva,  which  reduces  in 
to  a  soft  mass,  in  which  state  it  is  conveyed  into  the  stomach, 
where  it  is  more  completely  dissolved  by  the  gastric  juice. 

This  fluid  (which  is  secreted  into  the  stomach  by  appropri- 
ate glands)  is  so  powerful  a  solvent  that  scarcely  any  substan- 
ces will  resist  its  action. 

Emily.  The  coats  of  the  stomach,  however,  cannot  be  at- 
tacked by  it,  otherwise  we  should  be  in  danger  of  having  them 
destroyed  when  the  stomach  was  empty. 

.  'rs  B.  They  are  probably  not  subject  to  its  action  ;  as  long, 
at  least,  as  lift  continues.  But  it  appears,  that  when  the  gastric 
juice  has  no  foreign  substance  to  act  upon,  it  is  capable  of  oc- 
casioning a  degree  of  irritation  in  the  coats  ot  the  stomach, 
which  produces  the  sensation  of  hunger.  The  gastric  juice, 
together  with  the  heat  and  muscular  action  of  the  stomach, 
converts  the  aliment  into  an  uniform  pulpy  mass  called  chyme. 
This  passes  into  the  intestines,  where  it  meets  with  the  bile  and 
some  other  fluids,  by  the  agency  of  which,  and  by  the  opera- 
tion of  other  causes  hitherto  unknown,  the  chyme  is  changed 
into  chyle,  a  much  thinner  substance,  somewhat  resembling 
milk,  which  is  pumped  by  immense  numbers  of  small  absor- 
bent vessels  spread  over  the  internal  surface  of  the  intestines. 
These,  after  many  circumvolutions,  gradually  meet  and  unite 
into  large  branches,  till  they  at  length  collect  the  chyle  into 
one  vessel,  which  pours  its  contents  into  the  great  vein  near  the 
heart,  by  which  means  the  food,  thus  prepared,  enters  into  the 
circulation. 

Carolina.  But  I  do  not  yet  clearly  understand  how  the  blood, 


ON   RESPIRATION. 

thus  formed,  nourishes  the  body  and  supplies  all  the  secretions  ? 
Mrs.  />'.  Before  this  can  be  explained  to  you,  you  must  first 
allow  me  to  complete  the  formation  of  the  blood.  The  chyle 
may,  indeed,  be  considered  as  forming  the  chief  ingredient  of 
blood  ;  but  this  fluid  is  not  perfect  until  it  has  passed  through 
the  lungs,  and  undergone  (together  with  the  blood  that  has 
already  circulated)  certain  necessary  changes  that  are  effected 

by  RESPIRATION. 

Caroline.  I  am  very  glad  that  you  are  going  to  explain  the 
nature  of  respiration  :  I  have  often  longed  to  understand  it,  for 
though  we  talk  incessantly  of  breathing,  I  never  knew  pre- 
cisely what  purpose  it  answered. 

Mrs*  B.  It  is  indeed  one  of  the  most  interesting  processes 
imaginable;  but,  in  order  to  understand  this  function  well,  it 
will  be  necessary  to  enter  into  some  previous  explanations. 
Tell  me,  Emily, — what  do  you  understand  by  respiration? 

Emily.  Respiration,  I  conceive,  consists  simply  in  alternate- 
ly inspiring  air  into  the  lungs,  and  expiring  it  from  them. 

Mrs.  :t.  Your  answer  will  do  very  well  as  a  general  defini- 
tion. But,  in  order  to  form  a  tolerably  clear  notion  of  the  va- 
rious phenomena  of  respiration,  there  are  many  circumstances 
to  be  taken  into  consideration. 

In  the  first  place,  there  are  two  things  to  be  distinguished  in 
respiration,  the  mechanical  and  the  chemical  part  of  the  pro- 
cess. 

The  mechanism  of  breathing  depends  on  the  alternate  ex- 
pansions and  contractions  of  the  chest,  in  which  the  lungs  are 
contained.  When  the  chest  dilates,  the  cavity  is  enlarged,  and 
the  air  rushes  in  at  the  mouth,  to  fill  up  the  vacuum  formed  by 
this  dilatation,  when  it  contracts,  the  cavity  is  diminished,  and 
the  air  forced  out  again. 

Caroline.  I  thought  that  it  was  the  lungs  that  contracted  and 
expanded  in  breathing? 

Mrs.  B.  They  do  likewise ;  but  their  action  is  only  the  con- 
sequence of  that  of  the  chest.  The  lungs,  together  with  the 
heart  and  largest  blood  vessels,  in  a  manner  fill  up  the  cavity  of 
the  chest ;  they  could  not,  therefore,  dilate  if  the  chest  did  not 
previously  expand :  and,  on  the  other  hand,  when  the  chests 
contracts,  it  compresses  the  lungs  and  forces  the  air  out  of  them. 

Caraline.  The  lungs,  then,  are  like  bellows,  and  the  chest 
is  the  power  that  works  them. 

Mrs.  B.  Precisely  so.  Here  is  a  curious  little  figure  (PLATE 
XV.  fig.  5.,)  which  will  assist  me  in  explaining  the  mechanism 
of  breathing, 


308  OX    RESPIRATION. 

Caroline.  What  a  droll  figure !  a  little  head  fixed  upon  a 
glass  bell,  with  a  bladder  tied  over  the  bottom  of  it  ! 

Mrs.  B.  You  must  observe  that  there  is  another  bladder 
within  the  glass,  the  neck  of  vvhch  communicates  with  the 
mouth  of  the  figure — this  represents  the  lungs  contained  with- 
in the  chest;  the  other  bladder,  which  you  see  is  tied  loose, 
represents  a  muscular  membrane,  called  the  ctidpkragtn,  which 
separates  the  chest  from  the  lower  part  of  the  body.  By  the 
«hest,  therefore,  I  mean  that  large  cavity  in  the  upper  part  of 
the  body  contained  within  the  ribs,  the  neckj  and  the  dia- 
phragm ;  this  membrane  is  muscular,  and  capable  of  contrac- 
tion and  dilatation.  The  contraction  may  be  imitated  by  draw- 
ing the  bladder  tight  over  the  bottom  of  the  receiver,  when  the 
air  in  the  bladder,  which  represents  the  lungs,  will  be  forced 
out  through  the  mouth  of  the  figure — 

Emily.  See,  Caroline,  how  it  blows  the  flame  of  the  candle 
in  breathing  ? 

.Mrsk  7i.  By  letting  the  bladder  loose  again,  we  imitate  the 
dilatation  of  the  diaphragm,  and  the  cavity  of  the  chest  being 
enlarged,  the  lungs  expand,  and  the  air  rushes  in  to  fill  them. 

Emily.  This  figure,  I  think,  gives  a  very  clear  idea  of  the 
process  of  breathing. 

Mrs.  B.  It  illustrates  tolerably  well  the  action  of  the  lungs 
and  diaphragm  ;  but  those  are  not  the  only  powers  concerned 
in  the  enlargement  or  diminution  of  the  cavity  of  the  chest;  the 
ribs  are  also  possessed  of  a  muscular  motion  for  the  same  pur- 
pose; they  are  alternately  drawn  in,  edgeways,  to  assist  the 
contraction,  and  stretched  out,  like  the  hoops  of  a  barrel,  to 
contribute  to  the  dilatation  of  the  chest. 

Emily.  I  always  supposed  that  the  elevation  and  depression 
of  the  ribs  were  the  consequence,  not  the  cause  of  breathing. 

Mrs.  B.  It  is  exactly  the  reverse.  The  muscular  action  of 
the  diaphragm,  together  with  that  of  the  ribs,  are  the  causes  of 
the  contraction  and  expansion  of  the  chest ;  and  the  air  rush- 
ing into,  and  being  expelled  from  the  lungs,  are  only  consequen- 
ces of  those  actions. 

Caroline.  I  confess  that  I  thought  the  act  of  breathing  be- 
gan by  opening  the  mouth  for  the  air  to  rush  in,  and  that  it  was 
the  air  alone,  which,  by  alternately  rushing  in  and  out,  occa- 
sioned the  dilatations  and  contractions  of  the  lungs  and  chest. 
Mrs.  8,  Try  the  experiment  of  merely  opening  your  mouth  ; 
the  air  will  not  rush  in,  till  by  an  interior  muscular  action  you 
produce  a  vacuum — yes,  just  so,  your  diaphragm  is  now  dila- 
ted, and  the  ribs  expanded.  But  you  will  not  be  able  to  keep 
them  long  in  that  situation.  Your  lungs  and  chest  are  already 


ON    RESPIRATION. 

resuming;  their  former  state,  and  expelling  the  air  with  which 
they  had  just  been  filled.  This  mechanism  goes  on  more  or 
less  rapidly,  but,  in  general,  a  person  at  rest  and  in  health  will 
breathe  between  fifteen  and  twenty-five  times  in  a  minute. 

We  may  now  proceed  to  the  chemical  effects  of  respiration ; 
but,  for  this  purpose,  it  is  necessary  that  you  should  previously 
have  some  notion  of  the  circulation  of  the  blood.  Tell  me, 
Caroline,  what  do  you  understand  by  the  circulation  of  the 
blood  ? 

Caroline.  I  am  delighted  that  you  come  to  that  subject,  for 
it  is  one  that  has  long  excited  my  curiosity.  But  I  cannot  con- 
ceive how  it  is  connected  with  respiration.  The  idea  I  have  of 
the  circulation  is,  that  the  blood  runs  from  the  heart  through  tlie 
veins  all  over  the  body,  and  back  again  to  the  heart  ? 

Mrs.  B.  I  could  hardly  have  expected  a  better  definition 
from  you;  it  is,  however,  not  quite  correct,  for  you  do  not  dis- 
tinguish the  arteries  from  the  veins,  which,  as  we  have  already 
observed,  are  two  distinct  sets  of  vessels,  each  having  its  own 
peculiar  functions.  The  arteries  convey  the  blood  from  the 
heart  to  the  extremities  of  the  body  $  and  the  veins  bring  it 
back  into  the  heart. 

This  sketch  will  give  you  an  idea  of  the  manner  in  which 
some  of  the  principal  veins  and  arteries  of  the  human  body 
branch  out  of  the  heart,  which  may  be  considered  as  a  common 
centre  to  both  sets  of  vessels.  The  heart  is  a  kind  of  strong 
elastic  bag,  or  muscular  cavity,  which  possesses  a  power  of  di- 
lating and  contracting  itself,  for  the  purposes  of  alternately  re- 
ceiving and  expelling  the  blood,  in  order  to  carry  on  the  pro- 
cess of  circulation. 

Emily.  Why  are  the  arteries  in  this  drawing  painted  red, 
and  the  veins  purple  ? 

Mrs.  B.  It  is  to  point  out  the  difference  of  the  colour  of  the 
blood  in  these  two  sets  of  vessels. 

Caroline.  Bat  if  it  is  the  same  blood  which  flows  from  the 
arteries  into  the  veins,  how  can  its  colour  be  changed? 

Mrs.  B.  Thus  change  arises  from  various  circumstances.  In 
the  first  place,  during  its  passage  through  the  arteries,  the  blood 
undergoes  a  considerable  alteration,  some  of  its  constituent 
parts  being  gradually  separated  from  it  for  the  purposes  ef 
nourishing  the  body,  and  of  supplying  the  various  secretions. 
In  consequence  of  this,  the  florid  arterial  colour  of  the  blood 
changes  by  degrees  to  a  deep  purple,  which  is  its  constant  col- 
our in  the  veins.  On  the  other  hand,  the  blood  is  recruited 
during  its  return  through  the  veins  by  the  fresh  chyle,  or  im- 
perfect blood,  which  has  been  produced  by  food  ;  and  it  re- 


310  ON    RESPIRATION. 

ceives  also  lymph  from  the  absorbent  vessels,  as  we  have  be- 
fore mentioned.  After  having  undergone  these  several  chang- 
es, the  blood  returns  to  the  heart  in  a  state  very  different  from 
that  in  which  it  left  it.  It  is  loaded  with  a  greater  proportion 
of  hydrogen  and  carbon,  and  is  no  longer  fit  for  the  nourish- 
ment of  the  body,  or  other  purposes  of  circulation. 

Emily.  And  in  this  state  does  it  mix  in. the  heart  with  the 
pure  florid  blood  which  runs  into  the  arteries  ? 

Mrs.  B.  No.  The  heart  is  divided  into  two  cavities  or  corn- 
partitions,  called  the  right  and  left  ventricles.  The  left  ven- 
tricle is  the  receptacle  for  the  pure  arterial  blood  previous  to  its 
circulation  ;  whilst  the  venous,  or  impure  blood,  which  returns 
to  the  heart  after  having  circulated,  is  received  into  the  right 
ventricle,  previous  to  its  purification,  which  I  shall  presently 
explain. 

Caroline.  I  own  that  I  always  thought  the  same  blood  circu- 
lated again  and  again  through  the  body,  without  undergoing 
any  change. 

Mrs.  B.  Yet  you  must  have  supposed  that  the  blood  circu- 
lated for  some  purpose  ? 

Caroline.  I  knew  that  it  was  indispensable  to  life  ;  but  had 
no  idea  of  its  real  functions. 

Mrs.  B.  But  now  that  you  understand  that  the  blood  con- 
veys nourishment  to  every  part  of  the  body,  and  supplies  the 
various  secretions,  you  must  be  sensible  that  it  cannot  constant- 
ly answer  these  objects  without  being  proportionally  renovated 
and  purified. 

Emily.  But  does  not  the  chyle  answer  this  purpose  ? 

J\1rs.  B.  Only  in  part.  It  renovates  the  nutritive  principles 
of  the  blood,  but  does  not  relieve  it  from  the  superabundance  of 
water  and  carbon  with  which  it  is  encumbered. 

Emily.   How,  then,  is  this  effected  ? 

j\Jrs.  B.  By  RESPIRATION-  This  is  one  of  the  grand  myste- 
ries which  modern  chemistry  has  disclosed.  When  the  venous 
blood  enters  the  right  ventricle  of  the  heart,  it  contracts  by  its 
muscular  power,  and  throws  the  blood  through  a  large  vessel 
into  the  lungs,  which  are  contiguous,  and  through  which  it  cir- 
culates by  millions  of  small  ramifications.  Here  it  comes  in 
contact*  with  the  air  which  we  breathe.  The  action  of  the 
air  on  the  blood  in  the  lungs  is,  indeed,  concealed,  from  our 
immediate  observation  ;  but  we  are  able  to  form  a  tolerably  ac- 

*Xot  in  actual  contact.     In  this  case  it   i»  obvious    there    would  be 

nothing  to  confine  the  blood  and  prevent  its  flowing  out.     The  air  cells 

inarated  from  the  blood  vessels  by  an  extremely  thin   membrane. 

C, 


ON    RESPIRATION*  311 

curate  judgment  oi'it  from  the  changes  which  it  effects,  not  on- 
ly in  the  blood,  but  also  on  the  air  expired. 

The  air,  alter  passing  through  the  lungs,  is  found  to  contain 
all  the  nitrogen  inspired,  but  to  have  lost  part  of  its  oxygen,  and 
to  have  acquired  a  portion  of  watery  vapour  and  of  carbonic 
acid  gas.  Hence  it  is  inferred,  that  when  the  air  comes  in  con- 
tact with  the  venous  blood  in  the  lungs,  the  oxygen  attracts 
from  it  the  superabundant  quantity  of  carbon  with  which  it  has 
impregnated  itself  during  the  circulation,  and  converts  it  into 
carbonic  acid.  This  gaseous  acid,  together  with  the  redundant 
moisture  from  the  lungs,*  being  then  expired,  the  blood  is  re- 
stored to  its  former  purity,  that  is,  to  the  state  of  arterial  blood, 
and  is  thus  again  enabled  to  perform  its  various  functions. 

Caroline.  This  is  truly  wonderful !  Of  all  that  we  have  yet 
learned,  I  do  not  recollect  any  thing  that  has  appeared  to  me  so 
curious  and  interesting.  I  almost  believe  that  I  should  like  to 
study  anatomy  now,  though  I  have  hitherto  had  so  disgusting 
an  idea  of  it.  Pray,  to  whom  are  we  indebted  for  these  beauti- 
ful discoveries  ? 

Mrs.  B.  Priestley  and  Crawford,  in  this  country,  and  La- 
voisier, in  France,  are  the  principal  inventors  of  the  theory  of 
respiration.  Of  late  years  the  subject  has  been  farther  illustra- 
ted and  simplified  by  the  accurate  experiments  of  Messrs  Al- 
len and  Pepys.  But  the  still  more  important  and  more  admira- 
ble discovery  of  the  circulation  of  the  blood  was  made  long  be- 
fore by  our  immortal  countryman,  Harvey. 

Emily.  Indeed  I  never  heard  any  thing  that  delighted  me  so 
much  as  this  theory  of  respiration.  But  I  hope,  Mrs.  B.,  that 
you  will  enter  a  little  more  into  particulars  before  you  dismiss 
so  interesting  a  subject.  We  left  the  blood  in  the  lungs  to  un- 
dergo the  salutary  change  :  but  how  does  it  thence  spread  to 
all  the  parts  of  the  body  ? 

Mrs.  B.  After  circulating  through  the  lungs,  the  blood  is 
collected  into  four  large  vessels,  by  which  it  is  conveyed  into 
the  left  ventricle  of  the  heart,  whence  it  is  propelled  to  all  the 
different  parts  of  the  body  by  a  large  artery,  which  gradually 
ramifies  into  millions  of  small  arteries  through  the  whole  frame. 
From  the  extremities  of  these  little  ramifications  the  blood  is 
transmitted  to  the  veins,  which  bring  it  back  to  the  heart  and 
lungs,  to  go  round  again  and  again  in  the  manner  we  have 
just  described.  You  see,  therefore,  that  the  blood  actually  un- 
dergoes two  circulations  ;  the  one,  through  the  lungs,  by  which 

*  The  quantity  of  moisture  discharged  by  the  lungs  in  24  hours,  may 
be  computed  at  eight  or  nine  ounces, 


31:2  ON    RESPIRATION. 

it  is  converted  into  pure  arterial  blood  ;  the  other,  or  general 
circulation,  by  which  nourishment  is  conveyed  to  every  part  of 
the  body  :  and  ihese  are  both  equally  indispensible  to  the  sup- 
port of  anim-il  life. 

Emily.  But  whence  proceeds  the  carbon  with  which  the 
blood  is  impregnated  when  it  comes  into  the  lungs  ? 

Mrs.  />'.  Carbon  exists  in  a  greater  proportion  in  blood  than 
in  organised  animal  matter.  The  blood,  therefore,  after  sup- 
plying its  various  secretions,  becomes  loaded  with  an  excess  of 
carbon,  which  is  carried  off  by  respiration  ;  and  the  formation 
of  new  chyle  from  the  food  affords  a  constant  supply  of  carbo- 
naceous matter. 

Caroline.  I  wonder  what  quantity  of  carbon  may  be  expel- 
led from  the  blood  by  respiration  in  the  course  of  24  hours? 

Mrs.  B.  It  appears  by  the  experiments  of  Messrs.  Allen  and 
Pepys  that  about  40,000  cubic  inches  of  carbonic  acid  gas  are 
emitted  from  the  lungs  of  a  healthy  person,  daily;  which  is 
equivalent  to  eleven  ounces  of  solid  carbon  every  24  hours. 

Emily.  What  an  immense  quantity  !  And  pray  how  much 
of  carbonic  acid  gas  do  we  expel  from  our  lungs  at  each  expira- 
tion ? 

Mrs.  B.  The  quantity  of  air  which  we  take  into  our  lungs 
at  each  inspiration,  is  about  40  cubic  inches,  Which  contain  a 
little  less  than  10  cubic  inches  of  oxygen  ;  and  of  those  10  inch- 
es, one-eighth  is  converted  into  carbonic  acid  gas  on  passing 
once  through  the  lungs,*  a  change  which  is  sufficient  to  prevent 
air  which  has  only  been  breathed  once  from  suffering  a  taper 
to  burn  in  it. 

Caroline.  Pray,  how  does  the  air  come  in  contact  with  the 
blood  in  the  lungs  ? 

Mrs.  B.  I  cannot  answer  this  question  without  entering  into 
an  explanation  of  the  nature  and  structure  of  the  lungs.  You 
recollect  that  the  venous  blood,  on  being  expelled  from  the  right 
ventricle,  enters  the  lungs  to  go  through  what  we  may  call  the 
lesser  circulation  ;  the  large  trunk  or  vessel  that  conveys  it 
branches  out,  at  its  entrance  into  the  lungs,  into  an  infinite 
number  of  very  fine  ramifications.  The  windpipe,  which  con- 
veys the  air  from  the  mouth  into  the  lungs,  likewise  spreads 
out  into  a  corresponding  number  of  air  vessels,  which  follow 
the  same  course  as  the  blood  vessels,  forming  millions  of  very 
minute  air-cells.  These  two  sets  of  vessels  are  so  interwoven 
as  to  form  a  sort  of  net-work,  connected  into  a  kind  of  spongy 

*  The  bulk  of  carbonic  acid  gas  formed  by  respiration,  is  exactly 
t)ie  same  a<=  that  of  the  oxygen  gas  which  disappear?. 


ON    RESPIRATION.  &L3 

mass,  in  which  every  particle  of  blood  must  necessarily  come 
in  contact  with  a  particle  of  air. 

Caroline.  But  since  the  blood  and  the  air  are  contained  in 
different  vessels,  how  can  they  come  into  contact  ? 

J\>]rs.  ft.  They  acton  each  other  through  the  membrane  which 
forms  the  coats  of  these  vessels  ;  for  although  this  membrane 
prevents  the  blood  and  the  air  from  mixing  together  in  the 
lungs,  yet  it  is  no  impediment  to  their 'chemical  action  on  each 
other.* 

Emily.  Are  the  lungs  composed  entirely  of  blood  vessels  and 
air  vessels? 

J\lrs.  B.  I  believe  they  are,  with  the  addition  only  of  nerves 
and  of  a  small  quantity  of  the  cellular  substance  beforemention- 
ed,  which  connects  the  whole  into  an  uniform  mass. 

Emily.  Pray,  why  are  the  lungs  always  spoken  of  in  the  plu- 
ral number  ?  Are  there  more  than  one  ? 

'Mrs.B.  Yes;  for  though  they  form  but  one  organ,  they 
really  consist  of  two  compartments  called  lobes,  which  are  en- 
closed in  separate  membranes  or  bags,  each  occupying  one  side 
of  the  chest,  and  being  in  close  contact  with  each  other,  but 
without  communicating  together.  This  is  a  beautiful  provision 
of  nature,  in  consequence  of  which,  if  one  of  the  lobes  be 
wounded,  the  other  performs  the  whole  process  of  respiration 
till  the  first  is  healed. 

The  blood,  thus  completed,  by  the  process  of  respiration, 
forms  the  most  complex  of  all  animal  compounds,  since  it  con- 
tains not  only  the  numerous  materials  necessary  to  form  the  va- 
rious secretions,  as  saliva,  tears,  &c.  but  likewise  all  those  that 
are  required  to  nourish  the  several  parts  of  the  body,  as  the 
muscles,  bones,  nerves,  glands,  &c.t 

*  It  is  not  absolutely  certain  that  the  change  which  the  blood  under- 
goes in  the  lungs  is  entirely  owing  to  the  loss  of  carbon  ;  since  experi- 
ments show  that  any  animal  substance,  even  the  hand,  when  confined 
in  a  portion  of  atmospheric  air,  lessens  the  quantity  of  oxygen,  and 
produces  a  corresponding  quantity  of  carbonic  acid.  It  is  possible, 
then,  that  the  carbon  produced  by  respiration,  may  be  owing  merely 
to  the  contact  between  the  air  and  the  lungs.  C. 

t  The  process  of  secretion  does  not  consist  merely  in  the  separation 
of  certain  materials  from  the  blood  by  tne  secreting  organ  ;  but  in  ma- 
ny instances,  entirely  new  products  are  formed,  no  traces  of  which 
have  been  detected  in  the  blood.  For  instance  the  solid  matter  of  the 
bones  is  derived  from  the  blood,  yet  not  a  particle  ofphosphat  of  lime, 
(a  substance  composing  the  basis  of  bone,)  is  found  in  it.  It  appears, 
then,  that  the  glands  which  are  the  organs  of  secretion,  have  the  power 
of  producing  from  the  ultimate  atoms  of  the  blood,  the  variety  of  pro- 
peculiar  to  each.  Thus  the  glands  situated  about  the  eyes  ?r- 
28 


314  ON    RESPIRATION. 

Emily.  There  seems  to  be  a  singular  analogy  between  the 
blood -of  animals  and  the  sap  of  vegetables  ;  for  each  of  these 
fluids  contains  the  several  materials  destined  for  the  nutrition  of 
the  numerous  class  of  bodies  to  which  they  respectively  belong. 

Mrs.  B.  Nor  is  the  production  of  these  fluids  in  the  animal 
and  vegetable  systems  entirely  different ;  for  the  absorbent  ves- 
sels, which  pump  up  the  chyle  from  the  stomach  and  intestines, 
may  be  compared  to  the  absorbents  of  the  roots  of  plants,  which 
suck  up  the  nourishment  from  the  soil.  And  the  analogy  be- 
tween the  sap  and  the  blood  may  be  still  further  traced,  if  we 
follow  the  latter  in  the  course  of  its  circulation;  for,  in  the  liv- 
ing animal,  we  find  every  where  organs  which  are  possessed  of 
a  power  to  secrete  from  the  blood  and  appropriate  to  themselves 
the  ingredients  requisite  for  their  support. 

Caroline.  But  whence  do  these  organs  derive  their  respective 
powers  ? 

Mrs.  B.  From  a  peculiar  organisation,  the  secret  of  which 
no  one  has  yet  been  able  to  unfold.  But  it  must  be  ultimately 
by  means  of  the  vital  principle  that  both  their  mechanical  and 
chemical  powers  are  brought  into  action. 

I  cannot  dismiss  the  subject  of  circulation  without  mention- 
ing perspiration,  a  secretion  which  is  immediately  connected 
with  it,  and  acts  a  most  important  part  in  the  animal  economy. 

Caroline.  Is  not  this  secretion  likewise  made  by  appropriate 
glands  ? 

J\Jrs.  B.  No;  it  is  performed  by  the  extremities  of  the  arte- 
ries, which  penetrate  through  the  skin  and  terminate  under 
the  cuticle,  through  the  pores  of  which  the  perspiration  issues. 
When  this  fluid  is  not  secreted  in  excess,  it  is  insensible,  be- 
cause it  is  dissolved  by  the  air  as  it  exudes  from  the  pores  ;  but 
when  it  is  secreted  faster  than  it  can  be  dissolved,  it  becomes 
sensible,  as  it  assumes  its  liquid  state. 

Emily  This  secretion  bears  a  striking  resemblance  to  the 
transpiration  of  the  sap  of  plants.  They  both  consist  of  the 
most  fluid  parts,  and  both  exude  from  the  surface  by  the  ex- 
tremities of  the  vessels  through  which  they  circulate. 

Mrs.  B.  And  the  analogy  does  not  stop  there ;  for,  since  it 
has  been  ascertained  that  the  sap  returns  into  the  roots  of  the 
plants,  the  resemblance  between  the  animal  and  vegetable  cir- 
culation is  become  still  more  obvious.  The  latter,  however,  is 

Crete  the  tears,  a  saline,  pellucid  fluid  ;  while  the  liver  secretes,  from 
the  same  source  the  bile,  a  greenish,  opake,  bitter  and  extremely  nau- 
seous substance.  It  is  most  probable  that  we  shall  ever  remain  in  pro- 
found ignorance,  of  any  mode  of  imitating  these  operations.  C. 


ON    ANIMAL    HEAT.  315 

far  from  being  complete,  since,  as  we  observed  before,  it  con- 
sists only  in  u  rising  and  descending  of  the  sap,  whilst  in  ani- 
mals the  blood  actually  circulates  through  every  part  of  the 
system. 

We  have  now,  I  think,  traced  the  process  of  nutrition,  from 
the  introduction  of  the  food  into  the  stomach  to  its  finalty  beco- 
ming a  constituent  part  of  the  animal  frame.  This  will,  there- 
fore, be  a  fit  period  to  conclude  our  present  conversation. 

What  further  remarks  we  have  to  make  on  the  animal  econ- 
omy shall  be  reserved  for  our  next  interview. 


CONVERSATION  XXVI. 

ON  ANIMAL  HEAT;    AND  ON    VARIOUS  ANIMAL    PRO- 
DUCTS. 

Emily.  SINCE  our  last  interview,  I  have  been  thinking  much 
of  the  theory  of  respiration;  and  I  cannot  help  being  struck 
with  the  resemblance  which  it  appears  to  bear  to  the  process  of 
combustion.  For  in  respiration,  as  in  most  cases  of  combustion, 
the  air  suffers  a  change,  and  a  portion  of  its  oxygen  combines 
with  carbon,  producing  carbonic  acid  gas. 

Airs.  B.  I  am  much  pleased  that  this  idea  has  occurred  to 
you  :  these  two  processes  appear  so  very  analogous,  that  it  has 
been  supposed  that  a  kind  of  combustion  actually  takes  place 
in  the  lungs;  not  of  the  blood,  but  of  the  superfluous  carbon 
which  the  oxygen  attracts  from  it. 

Caroline.  A  combustion  in  our  lungs  !  that  is  a  curious  idea 
indeed!  But,  Mrs.  B.,  how  can  you  call  the  action  of  the  ah 
on  the  blood  in  the  lungs  combustion,  when  neither  light  nor 
heat  nre  produced  by  it? 

Emily.  I  was  going  to  make  the  same  objection. — Yet  I  do 
not  conceive  how  the  oxygen  can  combine  with  the  carbon,  and 
produce  carbonic  acid,  without  disengaging  heat  ? 

Mrs.  B.  The  fact  is,  that  heat  is  disengaged.*  Whether 
any  light  be  evolved,  I  cannot  pretend  to  determine ;  but  that 
heat  is  produced  in  considerable  and  very  sensible  quantities  is 
certain,  and  this  is  the  principal,  if  not  the  only  source  of  ANI- 
MAL HEAT. 

*  It  has  been  calculated  that  the  heat  produced  by  respiration  in  li! 
hours,  in  the  lungs  of  a  healthy  person,  is  such  as  would  aielt  about  100 
pounds  of  ice. 


>10  ON    ANIMAL    HEAT. 

Emily.  How  wonderful!  that  the  very  process  which  puri- 
ties and  elaborates  the  blood,  should  afford  an  inexhaustable 
supply  of  internal  heat  ? 

Mrs.  B.  This  is  the  theory  of  animal  heat  in  its  original  sim- 
plicity, such  nearly  as  it  was  first  proposed  by  Black  and  La- 
voisier. It  was  equally  clear  and  ingenious  ;  and  was  at  first 
generally  adopted.  But  it  was  objected,  on  second  considera- 
tion., that  if  the  whole  of  the  animal  heat  was  evolved  in  the 
lungs,  it  would  necessarily  be  much  less  in  the  extremities  ef 
the  body  than  immediately  at  its  source  ;  which  is  not  found 
to  be  the  case.  This  objection,  however,  which  was  by  no 
means  frivolous,  is  now  satisfactorily  removed  by  the  following 
consideration  : — Venous  blood  has  been  found  by  experiment  to 
have  less  capacity  for  heat  than  arterial  blood  ;  whence  it  fol- 
lows that  the  blood,  in  gradually  passing  from  the  arterial  to 
the  venus  state,  during  the  circulation,  parts  with  a  portion  of 
caloric,  by  means  of  which  heat  is  diffused  through  every  part 
of  the  body.* 

*  This  is  substantially  Dr.  Crawford's  theory  of  animal  heat ;  and 
that  it  is  a  most  beautiful  and  ingenions  one,  cannot  be  denied.  Sub- 
sequent experiments  have  however  proved  its  fallacy.  Dr.  John  Da- 
vy has  shown  that  the  difference  of  capacity  lor  heat  between  the  two 
kinds  of  blood  is  much  less  than  was  supposed  by  Dr.  Crawford — the 
capacity  of  arterial  being  only  one  per  cent,  above  that  of  venous 
blood.  Now  it  is  obvious,  that  this  minute  difference  cannot  account 
for  animal  temperature  ;  nor  is  it  certain  that  even  this  small  quantity 
of  heat  is  givfen  out  to  the  system.  Another  objection  is  the  result  of 
an  experiment  of  Mr.  Brodie.  This  indeed  seems  to  settle  the  ques- 
tion that  animal  heat  does  not  depend  on  any  change  which  the  blood 
undergoes  in  the  lungs.  He  found  that  on  keeping  up  an  artificial 
respiration  in  the  lungs  of  a  decapitated  animal,  the  blood  was  changed 
from  black  to  red,  and  carbonic  acid  was  given  out  as  usual ;  but  that 
the  animal  grew  cold  faster  than  another  dead  one,  where  such  artifi- 
cial respiration  was  not  kept  up. 

This,  it  is  obvious,  would  be  the  case  unless  heat  was  caused  by 
respiration,  as  the  air  forced  into  the  lungs  would  tend  to  cool  the  ani- 
mal. 

Prof.  Cooper  of  Philadelphia  proposes  another  theory.  <£  I  see  no 
material  difficulty,1'  says  he,  "'  in  accounting  for  the  production  of 
animal  heat  from  the  doctrine  of  latent  heat.  The  fluids  of  the  body 
are  incessantly  employed  to  renew  the,-s.olids  :  when  a  fluid  is  convert- 
ed into  a  solid,  heat  or  caloric  is  precipitated.  This  takes  place  eve- 
ry moment  very  gradually  in  every  part  of  the  system." 
"  We  are  ignorant  of  the  train  of  arguments  by  which  the  learned  Pro- 
;.'  supports  this  theory.  But,  if  on  the  one  hand,  the  conversion  of 
a  fluid  into  a  solid  produces  heat,  so  it  is  equally  well  proved,  that 
the  conversion  of  a  solid  into  a  fluid  produces  cold.  No-.v  the  solid 
parts  of  the.  body  after  being  deposited  from  the  fluids,  arc  again  con- 
yrr*ed  into  fluid*  bv  tlu;  nhaorbrni«,  Thi*  theory  then,  accb 


ON    ANIMAL    HEAT.  3 if 

More  and  more  admirable  ! 

Caroline.  The  cause  of  animal  heat  was  always  a  perfect 
mystery  to  me,  and  I  am  delighted  with  its  explanation. — -But 
pray,  Mrs.  B.,  can  you  tell  me  what  is  the  reason  of  the  in- 
crese  of  heat  that  takes  place  in  a  fever  ? 

Emily.  Is  it  not  because  we  then  breathe  quicker,  and  there- 
fore more  heat  is  disengaged  in  the  system  ? 

Mrs.  B.  That  may  be  one  reason:  but  I  should  think  that 
the  principal  cause  of  the  heat  experienced  in  fevers,  is,  that 
there  is  no  vent  for  the  caloric  which  is  generated  in  the  body. 
One  of  the  most  considerable  secretions  is  the  iiisensib]e  per- 
spiration ;  this  is  constantly  carrying  off  caloric  in  a  latent  state ; 
but  during  the  hot  stage  of  a  fever,  the  pores  are  so  contracted, 
that  all  perspiration  ceases,  and  the  accumulation  of  caloric  in 
the  body  occasions  those  burning  sensations  which  are  so  pain- 
ful. 

Emily.  This  is,  no  doubt,  the  reason  why  the  perspiration 
which  often  succeeds  the  hot  stage  of  a  fever  affords  so  m-ch 
relief.  If  I  had  known  this  theory  of  animal  heat  when  1  had 
a  fever  last  summer,  I  think  I  should  have  found  some  amuse- 
ment in  watching  the  chemical  processes  that  were  going  on 
within  me. 

Caroline.  But  exercise  likewise  produces  animal  heat,  and 
that  must  be  quite  in  a  different  manner. 

Mrs.  B.  Not  so  much  so  as  you  think;  for  the  more  exer- 
cise you  take,  the  more  the  body  is  stimulated,  anil  requires  re-, 
cruiting.  For  this  purpose  the  circulation  of  the  mood  is  quick- 
ened, the  breath  proportionably  accelerated,  and  consequently 
'i  greater  quantity  of  caloric  evolved. 

Caroline.  True  ;  after  running  very  fast,  I  gasp  for  breath, 

for  the  production  of  heat  only  when  the  deposition  is  greater  than  the 
absorption,  as  during  the  growth  of  the  system. 

From  some  experiments,  made  by  \]r.  Brodie  and  Dr.  Philip,  they 
have  been  induced  to  believe  that  animal  temperature  depends  on  the 
influence  of  the  nerves 

In  regard  to  this  tiieory  it  may  be  observed,  that  in  some  instances 
where  the  nervous  influence  seems  to  be  suspended,  the  heat  of  the 
part  remains  much  the  same  as  in  health. 

This  subject  has  excited  the  attention  of  the  learned  and  curious  ia 
all  ages,  and  a  great  variety  of  theories  have  been  offered  to  account 
for  it.  We  have  seen  none,  however,  to  which  insuperable  objections 
rnuy  not  be  brought.  We  must  therefore,  at  present,  be  contented 
v/ith  attributing  the  production  of  anirn\l  warmth  to  the  energies  of 
the  vital  principle;  leaving  it  to  future  generations  to  determine  and 
feline  its  immediate  cause.  CX 

28* 


318  ON    ANIMAL    Hi 

my  respiration  is  quick  and  hard,  and  it  is  just  then  that  I  begin 
to  feel  hot. 

Emily.  It  would  seem,  then,  that  violent  exercise  should 
produce  fever. 

Mrs.  B.  Not  if  the  person  is  in  a  good  state  of  health ;  for 
the  additional  caloric  is  then  carried  off  by  the  perspiration 
which  succeeds. 

Emily.  What  admirable  resources  nature  has  provided  for 
us  !  By  the  production  of  animal  heat  she  has  enabled  us  to 
keep  up  the  temperature  of  our  bodies  above  that  of  inani- 
mate objects  ;  and  whenever  this  source  becomes  too  abundant, 
the  excess  is  carried  off  by  perspiration. 

Mrs.  B.  It  is  by  the  same  law  of  nature  that  we  are  enabled,  - 
in  all  climates,  and  in  all  seasons,  to  preserve  our  bodies  of  an 
equal  temperature,  or  at  least  very  nearly  so. 

Caroline.  You  cannot  mean  to  say  that  our  bodies  are  of 
the  same  temperature  in  summer,  and  in  winter,  in  England., 
and  in  the  West-Indies. 

Mrs.  B.  Yes,  I  do  ;  at  least  if  you  speak  of  the  tempera- 
ture of  the  blood,  and  the  internal  parts  of  the  body ;  for  those 
which  are  immediately  in  contact  with  the  atmosphere,  such  as 
the  hands  and  face,  will  occasionally  get  warmer,  or  colder,  than 
the  internal  or  more  sheltered  parts.  If  you  put  the  bulb  of  a 
thermometer  in  your  mouth,  which  is  the  best  way  of  ascer- 
taining the  real  temperature  of  your  body,  you  will  scarcely 
perceive  any  difference  in  its  indication,  whatever  may  be  the 
difference  of  temperature  of  the  atmosphere. 

Caroline.  And  when  I  feel  overcome  by  heat,  I  am  really 
not  hotter  than  when  I  am  shivering  with  cold  ? 

Mrs.  B.  When  a  person  in  health  feels  very  hot,  whether 
from  internal  heat,  from  violent  exercise,  or  from  the  tempera- 
ture of  the  atmosphere,  his  body  is  certainly  a  little  warmer 
than  when  he  feels  very  cold  :  but  this  difference  is  much  smal- 
ler than  our  sensations  would  make  us  believe;  and  the  natur- 
al standard  is  soon  restored  by  rest  and  by  perspiration.  It  is 
chiefly  the  external  parts  that  are  warmer,  and  I  am  sure  that 
you  will  be  surprised  to  hear  that  the  internal  temperature  of 
the  body  scarcely  ever  descends  below  ninety-five  or  ninety-six 
degrees,  and  seldom  attains  one  hundred  and  four  or  one  hun- 
dred and  five  degrees,  even  in  the  most  violent  fevers. 

Emily.  The  greater  quantity  of  caloric,  therefore,  that  we 
receive  from  the  atmosphere  in  summer,  cannot  raise  the  tem- 
perature of  our  bodies  beyond  certain  limits,  as  it  does  that  of 
inanimate  bodies,  because  an  excess  of  caloric  is  carried  off  by 
perspiration. 


ON    ANIMAL    liEA-i.  3I<J 

Caroline.  But  the  temperature  of  the  atmosphere,  and  con- 
sequently that  of  inanimate  bodies,  is  surely  never  so  high  as 
that  of  animal  heat  ? 

Mrs.  B.  I  beg  your  pardon.  In  the  East  and  West  Indies, 
and  sometimes  in  the  southern  parts  of  Europe,  the  atmosphere 
is  frequently  above  ninety-eight  degrees,  which  is  the  common 
temperature  of  animal  heat.  Indeed,  even  in  this  country,  it  oc- 
casionally happens  that  the  sun's  rays,  setting  full  on  an  object, 
elevate  its  temperature  above  that  point. 

In  illustration  of  the  power  which  our  bodies  have  to  resist 
the  effects  of  external  heat,  Sir  Charles  Blagden,  with  some  oth- 
er gentlemen,  made  several  very  curious  experiments.  He  re- 
mained for  some  time  in  an  oven  heated  to  a  temperature  not 
much  inferior  to  that  of  boiling  water,  without  suffering  any 
other  inconvenience  than  a  profuse  perspiration,  which  he  sup- 
ported by  drinking  plentifully. 

Emily.  He  could  scarcely  consider  the  perspiration  as  an  in- 
convenience, since  it  saved  him  from  being  baked  by  giving  vent 
to  the  excess  of  caloric. 

Caroline.  1  always  thought,  I  confess,  that  it  was  from  the 
heat  of  the  perspiration  that  we  suffered  in  summer. 

Mrs.  B.  You  now  find  that  you  are  quite  mistaken.  When- 
ever evaporation  takes  place,  cold,  you  know,  is  produced  in 
consequence  of  a  quantity  of  caloric  being  carried  off  in  a  latent 
state ;  this  is  the  case  with  perspiration,  and  it  is  in  this  way 
that  it  affords  relief.  It  is  on  that  account  also  that  we  are  apt 
to  catch  cold,  when  in  a  state  of  profuse  perspiration.  It  is  for 
the  same  reason  that  tea  is  often  refreshing  in  summer,  though 
it  appears  to  heat  you  at  the  moment  you  drink  it. 

Emily.  And  in  winter,  on  the  contrary,  tea  is  pleasant  on 
account  of  its  heat. 

A'lrs.  B.  \  es  $  for  we  have  then  rather  to  guard  against  a 
deficiency  than  an  excess  of  caloric,  and  you  do  not  find  that 
tea  will  excite  perspiration  in  winter,  unless  after  dancing,  or 
any  other  violent  exercise. 

Caroline.  What  is  the  reason  that  it  is  dangerous  to  eat  ice 
after  dancing,  or  to  drink  any  thing  cold  when  one  is  very  hot  ? 

Mrs.  B.  Because  the  loss  of  heat  arising  from  the  perspira- 
tion, conjointly  with  the  chill  occasioned  by  the  cold  draught, 
produce  more  cold  than  can  be  borne  with  safety,  unless  you 
continue  to  use  the  same  exercise  after  drinking  that  you  did  be- 
fore 5  for  the  heat  occasioned  by  the  exercise  will  counteract* 
the  effects  of  the  cold  drink,  and  the  danger  will  be  removed. 
You  may,  however,  contrary  to  the  common  notion,  consider 
it  as  a  rule,  that  cold  liquids  may,  at  all  times,  be  drunk  with 


320  ON    ANIMAL    HEAT. 

perfett  safety,  however  hot  you  may  feel,*  provided  you  are 
not  at  the  moment  in  a  state  of  great  perspiration,  and  on  condi- 
tion that  you  keep  yourself  in  gentle  exercise  afterwards. 

Emily.  But  since  we  are  furnished  with  such  resources 
against  the  extremes  of  heat  or  cold,  I  should  have  thought  that 
all  climates  would  have  been  equally  wholesome. 

Mrs.  B.  That  is  true,  in  a  certain  degree,  with  regard  to 
those  who  have  been  accustomed  to  them  from  birth  ;  for  we 
find  that  the  natives  of  those  climates,  which  we  consider  as 
most  deleterious,  are  as  healthy  as  ourselves;  and  if  such  cli- 
mates are  unwholesome  to  those  who  are  habituated  to  a  more 
moderate  temperature,  it  is  because  the  animal  economy  does 
not  easily  accustom  itself  to  considerable  changes. 

Caroline.  But  pray,  Mrs.  B.,  if  the  circulation  preserves  the 
body  of  an  uniforn  temperature,  how  does  it  happen  that  ani- 
mals are  sometimes  frozen  ? 

J\-lrs.  B.  Because,  if  more  heat  be  carried  off  by  the  atmos- 
phere than  the  circulation  can  supply,  the  cold  will  finally  pre- 
vail, the  heart  will  cease  to  beat,  and  the  animal  will  be  frozen. 
And,  likewise,  if  the  body  remained  long  exposed  to  a  degree 
of  heat,  greater  than  the  perspiration  could  carry  of,  it  would 
at  last  lose  the  power  of  resisting  its  destructive  influence. 

Caroline.  Fish.  1  suppose,  have  no  animal  heat,  but  only 
partake  of  the  temperature  of  the  water  in  which  they  live  ?t 

Emily.  And  their  coldness,  no  doubt,  proceeds  from  their 
not  breathing  ? 

.Mrs.  B.  All  kinds  of  fish  breathe  more  or  less,  though  in  a 
much  .smaller  degree  than  )and  animals.  Nor  are  they  entire- 
ly destitute  of  animal  heat,  though,  for  the  same  reason,  they 
are  much  colder  than  other  creatures.  They  have  compara- 
tively but  a  very  small  quantity  of  blood,  therefore  but  very  lit- 
tle oxygen  is  required,  and  a  proportionally  small  quantity  of 
animal  heat  is  generated. 

Caroline.  But  how  can  fish  breathe  under  water  ? 

Mrs.  B.  They  breathe  by  means  of  the  air  which  is  dissolved 
in  the  water,  and  if  you  put  them  into  water  deprived  of  air 
by  boiling,  they  are  soon  suffocated. 

*  The  c  immou  notion  on  this  subject  is  certainly  the  most  safe.  A 
person  heated,  and  almost  exhausted  by  exercise  on  a  hot  day,  ought 
never  to  drink  any  cold  liquid,  except  in  very  small  quantities  at  a 
time.  Not  a  summer  passes  but  we  hear  of  deaths  by  drinking  cold 
water  after  violent  exercise.  C. 

t  Animals  belonging  to  tlia  order  Cetcc  of  Naturalists,  though  they  in- 
habit the  soa,  breathe  atmospheric  air,  and  have  hot,  red  blood,  Thi? 
order  includes  the  ivhales,  dolphins,  nanoals,  &c.  C, 


«N   ANIMAL    HEAT.  321 

If  a  fish  is  confined  in  a  vessel  of  water  closed  from  the  air, 
it  soon  dies  ;  and  any  fish  put  in  afterwards  would  be  killed  im- 
mediately, as  all  the  air  had  been  previously  consumed. 

Caroline.  Are  there  any  species  of  animals  that  breathe  more 
than  we  do  ? 

Mrs.  B.  Yes ;  birds,  of  all  animals,  breathe  the  greatest 
quantity  of  air  in  proportion  to  their  size  ;  and  it  is  to  this 
h  at  they  are  supposed  to  owe  the  peculiar  firmness  and 
strength  of  their  muscles,  by  which  they  are  enabled  to  support 
the  violent  exertion  of  flying. 

This  difference  between  birds  and  fish,  which  may  be  con- 
sidered as  the  two  extremes  of  the  scale  of  muscular  strength, 
is  well  worth  observing.  Birds  residing  constantly  in  the  at- 
mosphere, surrounded  by  oxygen,  and  respiring  it  in  greater 
proportions  than  any  other  species  of  animals,  are  endowed 
with  a  superior  degree  of  muscular  strength,  whilst  the  muscles 
of  fish,  on  the  contrary,  are  flaccid  and  oily  ;  these  animals  are 
comparatively  feeble  in  their  motions,  and  their  temperature  is 
scarcely  above  that  of  the  water  in  which  they  live.  This  is, 
in  all  probability,  owing  to  their  imperfect  respiration  5  the 
quantity  of  hydrogen  and  carbon,  that  is  in  consequence  accu- 
mulated in  their  bodies,,  fomrcthe  oil  which  is  so  strongly  char- 
acteristic of  that  species  of  animals,  and  which  relaxes  and 
softens  the  small  quantity  of  fibrine  which  their  muscles  con- 
tain. 

Caroline.  But,  Mrs.  B.,  there  are  some  species  of  birds  that 
frequent  both  elements,  as,  for  instance,  ducks  and  other  water 
fowl.  Of  what  nature  is  the  flesh  of  these  ? 

Mrs.  B.  Such  birds,  in  general,  make  but  little  use  of  their 
wings  ;  if  they  fly,  it  is  but  feebly,  and  only  to  a  short  distance. 
Their  flesh,  too,  partakes  of  the  oily  nature,  and  even  in  taste 
sometimes  resembles  that  of  fish.  This  is  the  case  not  only 
with  the  various  kinds  of  water  fowls,  but  with  all  other  am- 
phibious animals,  as  the  otter,  the  crocodile,  the  lizard,  &c. 

Caroline.  Arid  what  is  the  reason  that  reptiles  are  so  defi- 
cient in  muscular  strength  ? 

JWrs.  B.  It  is  because  they  usually  live  under  ground,  and 
seldom  come  into  the  atmosphere.  Tbey  have  imperfect,  and 
sometimes  no  discernible  organs  of  respiration  ;  they  partake, 
therefore,  of  the  soft  oily  nature  offish  ;  indeed,  many  of  them 
are  amphibious,  as  frogs,  toads,  and  snakes,  and  very  few  of 
them  find  any  difficulty  in  remaining  a  length  of  time  under 
water.*  Whilst,  on  the  contrary,  the  insect  tribe,  that  are  so 

*  Amphibious  animals  have  the  Denver  of  ?'i?pe:r1in;3r  respiration  for 


322  ON  ANIMAL  PRODUCTS. 

strong  in  proportion  to  their  size;  and  alert  in  their  motions, 
partake  of  the  nature  of  birds,  air  being  their  peculiar  element, 
and  their  organs  of  respiration  being  comparatively  larger  than 
in  other  classes  of  animals. 

I  have  now  given  you  a  short  account  of  the  principal  animal 
functions.  However  interesting  the  subject  may  appear  to 
you,  a  fuller  investigation  of  it  would,  I  fear,  lead  us  too  far  from 
our  object. 

Emily.  Yet  I  shall  not  quit  it  without  much  regret ;  for  of 
all  the  applications  of  chemistry,  these  appear  to  me  the  most 
curious  and  most  interesting. 

Caroline.  But,  Mrs.  B.,  I  must  remind  you  that  you  promi- 
sed to  give  us  some  account  of  the  nature  of  milk. 

Mrs.  B.  True.  There  are  several  other  animal  produc- 
tions that  deserve  likewise  to  be  mentioned.  We  shall  begin 
with  milk,  which  is  certainly  the  most  important  and  the  most 
interesting  of  all  the  animal  secretions. 

Milk,  like  all  other  animal  substances,  ultimately  yields  by- 
analysis  oxygen,  hydrogen,  carbon,  and  nitrogen.  These  are 
combined  in  it  under  the  forms  of  albumen,  gelatine,  oil,  and 
water.  But  milk  contains,  besides  a  considerable  portion  of 
phosphat  of  lime,  the  purposes  of  which  I  have  already  point- 
ed out. 

Caroline.  Yes ;  it  is  this  salt  which  serves  to  nourish  the 
tender  bones  of  the  suckling.  *» 

Mrs.  B.  To  reduce  milk  to  its  elements,  would  be  a  very 
complicated,  as  well  as  useless  operation  ;  but  this  fluid,  with- 
out any  chemical  assistance,  may  be  decomposed  into  three 
parts,  cream,  curds  and  whey.  These  constituents  of  milk 
have  but  a  very  slight  affinity  for  each  other,  and  you  find  ac- 
cordingly that  cream  separates  from  milk  by  mere  standing. 
It  consists  chiefly  of  oil,  which  being  lighter  than  the  other 
parts  of  the  milk,  gradually  rises  to  the  surface.  It  is  of  this, 
you  know,  that  butter  is  made,  which  is  nothing  more  than  ox- 
ygenated cream. 

Caroline.  Butter,  then,  is  somewhat  analogous  to  the  waxy 
.substance  formed  by  the  oxygenation  of  vegetable  oils. 

-Mrs.  B.  Very  much  so. 

Emily.  But  is  the  cream  oxygenated  by  churning  ? 

Mrs.  B.  Its  oxygenation  commences  previous  to  churning, 
merely  by  standing  exposed  to  the  atmosphere,  from  which  it 
absorbs  oxygen.  The  process  is  afterwards  completed  by 

a  considerable  timo.  It  is  in  consequence  of  this,  that  they  are  enabled 
to  live  under  water.     (J. 


ON    ANIMAL    PRODUCTS.  3%3 

churning ;  the  violent  motion  which  this  operation  occasions 
brings  every  particle  of  creani  in  contact  with  the  atmosphere, 
and  thus  facilitates  its  oxygenation. 

Caroline.  But  the  effect  of  churning,  I  have  often  observed 
in  the  dairy,  is  to  separate  the  creani  into  two  substances,  but- 
ter and  butter-milk. 

Mrs.  B.  That  is  to  say,  in  proportion  as  the  oily  particles  of 
the  cream  become  oxygenated,  they  separate  from  the  other 
constituent  parts  of  the  cream  in  the  form  of  butter.  So  by 
churning  you  produce,  on  the  one  hand,  butter,  or  oxygenated 
oil ;  and,  on  the  other,  butter-milk,  01  cream  deprived  of  oil. 
But  if  you  make  butter  by  churning  new  milk  instead  of  cream, 
the  butter-milk  will  then  be  exactly  similar  in  its  properties  to 
creamed  or  skimmed  milk. 

Caroline.  Yet  butter-milk  is  very  different  from  common 
skimmed  milk. 

Mrs.  B.  Because  you  know  it  is  customary,  in  order  to  save 
time  and  labour,  to  make  butter  from  cream  alone.  In  this 
case,  therefore,  the  butter-milk  is  deprived  of  the  creamed  milk, 
which  contains  both  the  curd  and  whey.  Besides,  in  conse- 
quence of  the  milk  remaining  exposed  to  the  atmosphere  du- 
ring the  separation  of  the  cream,  the  latter  becomes  more  or 
less  acid,  as  well  as  the  butter-milk  which  it  yields  in  churning. 

Emily.  Why  should  not  the  butter  be  equally  acidified  by 
oxygenation  ? 

.Mrs.  B.  Animal  oil  is  not  so  easily  acidified  as  the  other 
ingredients  of  milk.  Butter,  therefore,  though  usually  made  of 
sour  cream,  is  not  sour  itself,  because  the  oily  part  of  the  cream 
had  not  been  acidified.  Butter,  however^  is  susceptible  of  be- 
coming acid  by  an  excess  of  oxygen  ;  it  is  then  said  to  be  ran- 
cid, and  produces  the  sebacic  acid,  the  same  as  that  which  is 
obtained  from  fat. 

Emily.  If  that  be  the  case,  might  not  rancid  butter  be 
sweetened  by  mixing  with  it  some  substance  that  would  take 
the  acid  from  it  ? 

Mrs.  B.  This  idea  has  been  suggested  by  Sir  H.  Davy,  who 
supposes,  that  if  rancid  butter  were  well  washed  in  an  alkaline 
solution,  the  alkali  would  separate  the  acid  from  the  butter. 

Caroline.  You  said  just  now  that  creamed  milk  consisted  of 
curd  and  whey.  Pray  how  are  these  separated  ? 

Mrs.  B.  They  may  be  separated  by  standing  for  a  certain 
length  of  time  exposed  to  the  atmosphere  ;  but  this  decompo- 
sition may  be  almost  instantaneously  effected  by  the  chemical 
agency  of  a  variety  of  substances.  Alkalies,  rennet,*  and  in- 

*  Rennet  is  the  name  given  to  a  watery  infusion  of  the  coats  of  thf 


324  OK   ANIMAL    PRODUCTS. 

deed  almost  all  animals  substances,  decompose  milk  by  combi 
ning  with  the  curds. 

Acids  and  spirituous  liquors,  on  the  other  hand,  produce  ;i 
decomposition  by  combining  with  the  whey.  In  order,  there- 
fore, to  obtain  the  whey  pure,  rennet,  or  alkaline  substances^ 
must  be  used  to  attract  the  curds  from  it. 

But  if  it  be  wished  to  obtain  the  curds  pure,  the  whey  must 
be  separated  by  acids,  wine,  or  other  spiritous  liquors. 

Emily.  This  is  a  very  useful  piece  of  information ;  for  I 
tind  white-wine  whey,  which  I  sometimes  take  when  I  have  a 
cold,  extremely  heating;  now,  if  the  whey  were  separated  by 
means  of  an  alkali  instead  of  wine,  it  would  not  produce  that 
effect. 

Mrs.  B.  Perhaps  not.  But  I  would  strenuously  advise  you 
not  to  place  too  much  reliance  on  your  slight  chemical  knowl- 
edge in  medical  matters.  I  do  not  know  why  whey  is  not  sep- 
arated from  curd  by  rennet,  or  by  an  alkali,  for  the  purpose 
which  you  mention  ;  but  I  strongly  suspect  that  there  must  be 
some  good  reason  why  the  preparation  by  means  of  wine  is 
generally  preferred.  I  can,  however,  safely  point  out  to  you  a 
method  of  obtaining  whey  without  either  alkali,  rennet,  or 
wine;  it  is  by  substituting  lemon  juice,  a  very,  small  quantity 
of  which  will  separate  it  from  the  curds. 

Whey,  as  an  article  of  diet,  is  very  wholesome,  being  re- 
markable light  of  digestion.  But  its  effect,  taken  medicinally, 
is  chiefly,  I  believe,  to  excite  perspiration,  by  being  drunk  warm 
on  going  to  bed. 

From  whey  a  substance  may  be  obtained  in  crystals  by  evap- 
oration, called  sugar  of  milk.  This  substance  is  sweet  to  the 
taste,  and  in  its  composition  is  so  analogous  to  common  sugar, 
that  it  is  susceptible  of  undergoing  the  vinous  fermentation. 

Caroline.  Why  then  is  not  wine,  or  alcohol,  made  from 
whey  ? 

Mrs.  B.  The  quantity  of  sugar  contained  in  milk  is  so  tri- 
fling, that  it  can  hardly  answer  that  purpose.  I  have  heard  of 
only  one  instance  of  its  being  used  for  the  production  of  a  spir- 
ituous liquor,  and  this  is  by  the  Tartan  Arabs ;  their  abund- 
ance of  horses,  as  well  as  their  scarcity  of  fruits,  has  introduced 
the  fermentation  of  mares'  milk,  by  which  they  produce  a  li- 
quor called  koumiss.  Whey  is  likewise  susceptible  of  being 
acidified  by  combining  with  oxygen  from  the  atmosphere.  It 

stomach  of  a  sucking  calf.  Its  remarkable  efficacy  in  promoting  co- 
agulation is  supposed  to  depend  on  the  gastric  juice  with  which  it  is 
Jmprejrnated. 


«N  ANIMAL  PRODUCTS. 

then  produces  the  lactic  aoid,  which  you  may  recollect  is  class- 
ed with  the  animal  acids,  as  the  acid  of  milk. 

Let  us  now  see  what  are  the  properties  of  curds. 

Emily.  I  know  that  they  are  made  into  cheese  ;  but  I  have 
heard  that  for  that  purpose  they  are  separated  from  the  whey 
by  rennet,  and  yet  this  you  have  just  told  us  is  not  the  method 
of  obtaining  pure  curds  ? 

Mrs.  B.  Nor  are  pure  curds  so  well  adapted  for  the  forma- 
tion of  cheese.  For  the  nature  and  flavour  of  the  cheese  de- 
pend, in  a  great  measure,  upon  the  cream  or  oily  matter  which 
is  left  in  the  curds  ;  so  that  if  every  particle  of  cream  be  remov- 
ed from  the  curds,  the  cheese  is  scarcely  eatable.  Rich  chees- 
es, such  as  cream  and  Stilton  cheeses,  derive  their  excellence 
from  the  quantity,  as  well  as  the  quality,  of  the  cream  that  en- 
ters into  their  composition. 

Caroline.  I  had  no  idea  that  milk  was  such  an  interesting 
compound.  In  many  respects  there  appears  to  me  to  be  a  very 
striking  analogy  between  milk  and  the  contents  of  an  egg,  both 
in  respect  to  their  nature  and  their  use.  They  are,  each  of 
them,  composed  of  the  various  substances  necessary  for  the 
nourishment  of  the  young  animal,  and  equally  destined  for  that 
purpose. 

Mrs  B.  There  is  however,  a  very  essential  difference.  The 
young  animal  is  formed,  as  well  as  nourished,  by  the  contents 
of  the  egg-shell ;  whilst  milk  serves  as  nutriment  to  the  suck- 
ling, only  after  it  is  born. 

There  are  several  peculiar  animal  substances  which  do  not 
enter  into  the  general  enumeration  of  animal  compounds,  and 
which,  however,  deserve  to  be  mentioned. 

Spermaceti  is  of  this  class;  it  is  a  kind  of  oily  substance  ob- 
tained from  the  head  of  the  whale,  which,  however,  must  un- 
dergo a  certain  preparation  before  it  is  in  a  fit  state  to  be  made 
into  candles.  It  is  not  much  more  combustible  than  tallow,  but 
it  is  pleasanter  to  burn,  as  it  is  less  fusible  and  less  greasy. 

Ambergris  is  another  peculiar  substance  derived  from  a  spe- 
cies of  whale.  It  is,  however,  seldom  obtained  from  the  ani- 
mal itself,  but  is  generally  found  floating  on  the  surface  of  the 
sea. 

Wax,  you  know,  is  a  concrete  oil,  the  peculiar  product  of  the 
bee,  part  of  the  constituents  of  which  may  probably  be  derived 
from  flowers,  but  so  prepared  by  the  organs  of  the  bee,  arid  so 
mixed  with  its  own  substance,  as  to  be  decidedly  an. animal  pro- 
duct. Bees'  wax  is  naturally  of  a  yellow  colour,  but  it  is  bleach- 
ed by  long  exposure  to  the  atmosphere,  or  may  be  instantane- 
ously whitened  by  the  oxy-muriatic  acid.  The  combustion  & 
20 


326  ON  ANIMAL  PRODUCTS. 

wax  is  far  more  perfect  than  that  of  tallow,  and  consequently 
produces  a  greater  quantity  of  light  and  heat. 

Lac  is  a  substance  very  similar  to  wax  in  the  manner  of  its 
formation  ;  it  is  the  product  of  an  insect,  which  collects  its  in- 
gredients from  flowers,  apparently  for  the  purpose  of  protecting 
its  eggs  from  injury.  It  is  formed  into  cells,  fabricated  with  as 
much  skill  as  those  of  the  honey-comb,  but  differently  arrang- 
ed. The  principal  use  of  lac  is  in  the  manufacture  of  sealing- 
wax,  and  in  making  varnishes  and  lacquers. 

Musk,  civet,  and  castor,  are  other  particular  productions, 
from  different  species  of  quadrupeds.  The  two  first  are  very 
powerful  perfumes  :  the  latter  has  a  nauseous  smell  and  taste, 
and  is  only  used  medicinally. 

Caroline.  Is  it  from  this  substance  that  castor  oil  is  obtain- 
ed ? 

Mrs.  B.  No.  Far  from  it,  for  castor  oil  is  a  vegetable  oil, 
expressed  from  the  seeds  of  a  particular  plant ;  and  has  not  the 
least  resemblance  to  the  medicinal  substance  obtained  from  the 
castor. 

Silk  is  a  peculiar  secretion  of  the  silk-worm,  with  which  it 
builds  its  nest  or  cocoon.  This  insect  was  originally  brought 
to  Europe  from  China.  Silk,  in  its  chemical  nature,  is  very 
similar  to  the  hair  and  wool  of  animals;  whilst  in  the  insect  it 
is  a  fluid,  which  is  coagulated,  apparently  by  uniting  with  oxy- 
gen, as  soon  as  it  comes  in  contact  with  the  air.  The  moth  of 
the  silk-worm  ejects  a  liquor  which  appears  to  contain  a  pecu- 
liar acid,  called  bombic,  the  properties  of  which  are  but  very 
little  known. 

Emily.  Before  we  conclude  the  subject  of  the  animal  econo- 
my, shall  we  not  learn  by  what  steps  dead  animals  return  to 
their  elementary  state  ? 

Mrs.  B.  Animal  matter,  although  the  most  complicated  of 
all  natural  substances,  returns  to  its  elementary  state  by  one 
single  spontaneous  process,  the  putrid  fermentation.  By  this, 
the  albume^  fibrine,  &c.  are  slowly  reduced  to  the  state  of  ox- 
vgen,  hydrogen,  nitrogen,  and  carbon;  and  thus  the  circle  of 
changes  through  which  these  principles  have  passed  is  finally 
completed.  They  first  quitted  their  elementary  form,  or  their 
combination  with  unorganised  matter,  to  enter  into  the  vegeta- 
ble system.  Hence  they  were  transmitted  to  the  animal  king- 
dom ;  and  from  this  they  return  again  to  their  primitive  simpli- 
city, soon  to  re-enter  the  sphere  of  organised  existence. 

When  all  the  circumstances  necessary  to  produce  fermenta- 
tion do  not  take  place,  animal,  like  vegetable  matter,  is  liable 
to  a  partial  or  imperfect  decomposition,  which  converts  it  into 
a  combustible  substance  very  like  spermaceti,  I  dare  say  that 


ON  ANIMAL  PRODUCTS.  32? 

Caroline,  who  is  so  fond  of  analogies,  will  consider  this  as  a 
kind  of  animal  bitumen. 

Caroline.  And  why  should  I  not,  since  the  processes  which 
produce  these  substances  are  so  similar  ? 

Mrs.  B.  There  is,  however,  one  considerable  difference ;  the 
state  of  bitumen  seems  permanent,  whilst  that  of  animal-sub- 
stances, thus  imperfectly  decomposed,  is  only  transient ;  and 
unless  precautions  be  taken  to  preserve  them  in  that  state,  a  to- 
tal dissolution  infallibly  ensues.  This  circumstance,  of  the  oc- 
casional conversion  of  animal  matter  into  a  kind  of  sperma- 
ceti, is  of  late  discovery.  A  manufacture  has  in  consequence 
been  established  near  Bristol,  in  which,  by  exposing  the  carca- 
ses of  horses  and  other  animals  for  a  length  of  time  under  wa- 
ter, the  muscular  parts  are  converted  into  this  spermaceti-like 
substance.  The  bones  afterwards  undergo  a  different  process 
to  produce  hartshorn,  or  more  properly,  ammonia,  and  phos- 
phorus ;  and  the  skin  is  prepared  for  leather. 

Thus  art  contrives  to  enlarge  the  sphere  of  useful  purposes, 
for  which  the  elements  were  intended  by  nature ;  and  the  pro- 
ductions of  the  several  kingdoms  are  frequently  arrested  in. 
their  course,  and  variously  modified,  by  human  skill,  which 
compels  them  to  contribute,  under  new  forms,  to  the  necessi- 
ties or  luxuries  of  man. 

But  all  that  we  enjoy,  whether  produced  by  the  spontaneous 
operations  of  nature,  or  the  ingenious  efforts  of  art,  proceed 
alike  from  the  goodness  of  Providence. — To  GOD  alone  man 
owes  the  admirable  faculties  which  enable  him  to  improve  and 
modify  the  productions  of  nature,  no  less  than  those  produc- 
tions themselves.  In  contemplating  the  works  of  the  creation, 
or  studying  the  inventions  of  art ;  let  us,  therefore,  never  foi- 
get  the  Divine  Source  from  which  they  proceed  ;  and  thus 
every  acquisition  of  knowledge  will  prove  a  lesson  of  piety 
and  virtue. 


DESCRIPTION  OP  TH£ 


DESCRIPTION  OF  THE  APHLOGISTIC,  OR  FLAMt.- 
LESS  LAMP. 

BV  DR.  J.  L.  COMSTOCK,  OP  HARTFORD. 

IN  the  construction  of  this  Lamp,  the  object  is  to  keep  a  coil 
of  wire  in  a  state  of  ignition,  without  either  flame  or  smoke. 

The  principle  on  which  it  is  constructed,  I  believe,  was  first 
discovered  by  Sir  H.  Davy.  He  found  that  on  heating  the  end 
of  a  piece  ofptatina  wire  red  hot,  and  instantly  holding  it  near 
the  surface  of  some  ether 9  placed  in  a  wine  glass,  the  wine  was 
kept  at  a  red  heat  as  long  as  the  experiment  was  continued. 

Whether  Sir  Humphrey  pursued  the  subject  any  further,  I 
am  not  informed.  It  is  most  probable  however  that  he  did  not, 
as  it  is  stated  in  a  London  paper  of  the  last  year,  that  Prof.  Ure 
of  Glasgow  had  determined  the  circumstances  which  modify 
the  performance  of  the  lamp,  and  that  one  constructed  by  him 
was  in  full  operation  in  that  city  (London)  and  had  excited 
much  public  curiosity.  This  notice  contained  some  directions, 
concerning  the  size  of  the  wire,  to  be  used,  and  the  manner  of 
coiling  it.  I  have  however  seen  no  description  of  this  lamp 
which  would  enable  one  readily  to  construct  it.  The  following 
may  therefore  interest  such  readers,  as  have  seen  an  account  of 
so  curious  a  discovery. 

The  principle  on  which  the  aphlogistic  lamp  is  constructed 
involves  two  conditions,  which  are  absolutely  requisite,  viz. 
that  we  make  use  of  a  combustible  substance  which  evaporates 
at  a  low  degree  of  heat,  and  a  metal  which  is  a  bad  conductor 
of  caloric.  For  the  combustible,  alcohol  seems  best  suited  to 
this  purpose.  Sulphuric  ether,  aside  from  its  high  price,  and 
disagreeable  smell,  I  have  sometimes  found  to  fail ;  the  igni- 
tion ceasing  without  any  obvious  cause. 

In  regard  to  the  metal,  gold  and  silver,  both  fail  in  conse- 
quence of  the  rapidity  with  which  they  conduct  caloric.  Silver, 
toy,  would  soon  be  destroyed  by  the  intense  heat.  Iron,  al- 
though so  bad  a  conductor,  as  to  remain  ignited  for  a  time,  soon 
fails,  being  converted  into  red  oxide.  Platina  seems  to  be  the 
only  metal  adapted  to  our  purpose,  being  a  slow  conductor  of 
caloric,  and  not  easily  oxidated  at  the  highest  temperatures. 

This  is  to  be  drawn  into  wire  of  56-100  or  60-100  of  an 
inch  in  diameter,  being  about  the  size  of  card,  or  brass  wire, 
No.  26.  Experience  has  shown  that  this  size  succeeds  better 
than  any  other.  If  larger,  the  heat  is  carried  off  too  fast,  and 
the  ignition  ceases.  4f  much  finer,  it  does  not  retain  sufficient 


APHLOGISTIC    LAMP.  329 

heat  at  the  lower  part  of  the  coil  to  keep  up  the  evaporation  of 
the  alcohol  from  the  wick. 

The  coiling  of  the  wire,  and  the  adjustment  of  the  wick,  are 
the  most  difficult  parts  of  the  construction. 

The  coil  A.  fig.  1.  (frontispiece)  is  made  by  winding  the  wire 
round  a  piece  of  wood,  cut  of  the  proper  size,  and  shape.  The 
size  is  determined  by  the  bore  of  the  glass  tube,  allowing  for  the 
diameter  of  the  wire.  The  shape  is  plane  cylindrical  in  that 
part  which  enters  the  tube  ;  and  slightly  conical  where  it  pro- 
jects above  the  tube,  as  seen  in  the  figure.  (I  believe  this  is 
the  best  shape,  though  I  have  succeeded  as  well  when  the  coil 
was  of  the  same  shape  throughout.) 

In  winding  the  coil,  it  is  best  that  the  turns  of  the  wire  should 
come  in  contact.  Afterwards  it  is  to  be  gently  extended,  so  as 
to  leave  the  turns  as  nearly  as  possible  to  each  other,  without 
touching. 

The  diameter  of  the  coil  is  about  one-sixth  of  an  inch  where 
it  enters  the  tube.  Its  length  half  an  inch,  or  a  little  less,  con- 
taining from  twenty  to  thirty  turns  of  the  wire.  The  projection 
above  the  tube  is  about  one  half  of  the  length. 

B.  Fig.  1.  is  a  glass  tube,  containing  a  cotton  wick,  which  by 
capillary  attraction  carries  the  alcohol  up  to  the  platina  coil. 
The  length  of  this  is  arbitrary,  being  from  one  to  three  or  four 
inches.  The  bore  is  about  the  sixth  of  an  inch,  so  as  barely  to 
admit  the  coil.  The  wick,  consisting  of  eight  or  ten  threads, 
is  first  drawn  through  the  tube,  and  then  introduced  about  half 
wa>  into  the  coil,  so  as  to  come  even  with  the  top  of  the  tube. 
This  requires  very  nice  adjustment.  If  the  wick  is  too  high,  the 
wire  is  rapidly  cooled  by  the  alcohol,  and'  ignition  ceases  in  a 
few  moments.  If  too  low,  the  evaporation  by  the  heat  of  the 
wire  is  insufficient.  If,  however,  the  other  parts  are  well  con- 
structed, a  few  trials  will  ensure  success. 

Fig.  2.  shows  the  lamp  complete.  The  body  of  it  is  a  low 
vial,  or  inkstand,  capable  of  holding  about  two  ounces  of  alco- 
hol. It  is  stopped  accurately  with  a  cork,  which  is  covered,  for 
ornament,  with  tin  foil.  The  aperture  for  admitting  the  tube 
and  wick,  is  make  with  a  hot  iron. 

D.  is  a  small  tube  through  which  the  alcohol  is  poured.  A 
dropping  tube  is  convenient  for  this  purpose,  but  a  small  funnel 
is  easily  made  by  cutting  off  an  inch  of  the  neck  of  a  broken  re- 
tort, into  which  is  pushed  a  cork,  and  through  this  a  small 
quill.  Another  orifice  still,  for  letting  off  the  air,  as  the  alco- 
hol goes  in,  may  be  made  through  the  cork.  The  orifices,  of 
course,  are  to  be  stopped,  to  prevent  evaporation,  after  the  lamp 
is  charged. 

29* 


330  DESCRIPTION,    &C. 

When  the  lamp  is  completed  and  charged,  the  alcohol  is  in- 
flamed  by  holding  the  coil  in  the  blaze  of  a  candle.  After  let- 
ting it  burn  fora  few  minutes,  the  flame  is  blown  out,  when,  if 
every  thing  is  properly  adjusted,  the  wire  will  continue  red  hot 
until  the  alcohol  is  exhausted. 

The  explanation  why  the  ignition  of  the  wire  is  permanent, 
seems  to  be  sufficiently  simple.  Alcohol,  when  in  the  state  oi 
vapour,  combines  with  oxygen  with  great  facility.  The  tem- 
perature of  the  wire  is  first  raised  by  the  flame  of  the  candle  to 
about  600  degrees',  Fahrenheit.  This  degree  of  heat  is  such  as 
to  effect  the  combustion  of  the  alcohol  with  the  oxygen  of  the 
atmosphere.  When  this  is  once  effected,  the  caloric  extricated 
by  the  combustion  of  the  alcohol,  is  sufficient  to  keep  the  coil 
at  a  red  heat,  which  again  is  the  temperature  at  which  the  alco- 
hol is  combustible,  so  that  one  portion  of  alcohol  by  the  absorp- 
tion of  oxygen,  and  the  consequent  extrication  of  heat,  lavs  the 
foundation  for  the  combustion  of  another  portion  :  and  as  the 
alcohol  rises  in  a  constant  stream,  so  the  effect  is  constant. 
The  stream  of  vapour  is  much  increased  by  the  heat  of  the  low- 
er part  of  the  coil,  where  it  embraces  the  wick,  and  the  tem- 
perature of  the  alcohol  is  increased  before  it  reaches  the  part  of 
the  coil  where  combustion  is  effected.  Sometimes  the  last,  or 
upper  turn  of  the  wire  only  is  kept  red  hot. 

This  lamp,  though  one  of  the  most  curious  inventions  of  the 
age,  is  not  merely  a  curiosity.  The  facility  and  certainty  with 
which,  by  means  of  a  match,  a  light  may  be  obtained  from  it, 
constitutes  its  utility.  The  proper  matches  for  this  purpose  are 
prepared  by  dipping  the  common  brimstone  matches  into  a 
paste  made  by  mixing  two  parts  of  white  sugar  with  one  part  of 
chlorate  (oxymuriat)  of  potash.  The  red  French  matches  are 
ofthis  kind,  and  answer  the  purpose  completely. 

In  cases  where,  a  light  might  be  wanted,  but  a  constant  one 
would  be  offensive,  this  lamp  might  be  a  great  convenience  ;  a 
light  being  immediately  obtained  by  merely  touching  a  match 
to  the  platina  coil,  and  then  to  the  wick  of  the  candle.  Physi- 
cians or  others  who  are  liable  to  be  called  up  in  the  night  would 
also  find  it  convenient. 

The  aphlogistic  lamp,  with  the  proper  matches  may  be  ob- 
tained at  Mr.  Charles  Hosmer's  Variety  Store  in  this  city. 


QUESTIONS  FOR  EXERCISE. 


CONVERSATION  I. 

WHAT  is  the  object  of  Chemistry  ? 
What  is  an  elementary  substance  ? 
What  is  decomposition  ? 

What  is  the  difference  between  decomposition  and  division? 
What  is  a  compound  body  ? 
What  is  the  number  of  elementary  substances  ? 
What  is  the  difference  between  attraction  of  cohesion,  and  at- 
traction of  composition  ? 
How  can  a  compound  body  be  decomposed  ? 
What  are  the  names  and  number  of  the  simple  bodies  ? 

CONVERSATION  II. 

Is  there  an  inseparable  connection  between  light  and  heat  ?— 
How  can  they  be  separated  ? 

To  what  is  the  phosphorescence  of  dead  animal  matter  owing  ? 

How  do  you  distinguish  heat  and  light  from  each  other  ? 

What  is  free  caloric? 

Wiiat  is  combined  or  latent  caloric  ? 

What  is  the  difference  between  heat  and  caloric  ? 

What  is  the  most  remarkable  effect  of  free  caloric  on  bodies  ? 

Does  heat  expand  all  bodies  in  the  same  degree? 

What  is  the  temperature  of  boiling  water  ? 

Why  cannot  water  be  heated  above  a  certain  degree  in  the  open 
air? 

Why  was  the  freezing  point  of  Fahrenheit  marked  32°  ? 

Why  do  air  thermometers  indicate  smaller  changes  of  tempera- 
ture than  others  ? 

Can  you  name  any  substance,  or  any  known  condition  of  a  sub- 
stance in  which  caloric  is  absent  ? 

What  is  cold  ? 

Why  does  a  metallic  mirror  feel  cold  when  placed  before  the 
fire? 

What  kind  of  a  surface  radiates  most  heat  ? 

Why  do  metallic  coffee  pots  retain  the  heat  of  the  coffee  longer 
than  earthen  ones  ? 

What  becomes  of  the  caloric  radiated  by  a  hot  body  ? 


332  QUESTIONS. 

What  is  the  difference  between  the  radiation  and  reflection  of 
caloric  ? 

CONVERSATION  III. 

Why  do  some  substances  feel  hotter,  or  colder,,  than  others,  at 
the  same  temperature  ? 

Do  fluids  conduct  caloric  downwards  ? 

How  are  fluids  heated  when  placed  over  a  fire  ? 

Why  does  water  first  freeze  at  the  surface  ? 

Why  does  not  the  surface  of  the  sea  freeze  ? 

Why  does  a  fire  heat  glass,  when  the  sun  does  not  ? 

Why,  in  the  summer,  is  it  particularly  hot  in  cloudy,  or  foggy 
weather? 

Why  is  the  wind  cooling  to  our  bodies  ? 

Does  water  boil  from  the  top,  or  bottom  of  the  vessel  ? 

What  are  the  principle  solvent  fluids  ? 

What  is  the  difference  between  solution  and  mixture  ? 

Is  a  fluid  increased  in  bulk  by  the  solution  of  a  solid  1 

When  is  a  solvent  saturated? 

What  is  evaporation  ? 

When  does  the  air  contain  most  moisture  ?  in  winter  or  sum- 
mer ? 

How  do  you  account  for  the  formation  of  dew  ? 

Why  is  a  glass  of  cold  water  covered  with  moisture  in  hot 
weather  ? 

Why  does  the  evaporation  of  ether  freeze  water  ? 

How  does  ignition  differ  from  combustion  ? 

CONVERSATION  IV. 

What  is  understood  by  capacity  for  caloric  ? 
Have  all  bodies  of  the  same  weight  the  same  capacity  for  ca- 
loric ? 

How  is  the  capacity  of  bodies  for  heat  ascertained  ? 
What  is  latent  caloric  ? 

How  does  latent  caloric  differ  from  specific  caloric  ? 
Why  does  not  the  thermometer  rise  in  a  warm  room,  when  its 
.    bulb  is  in  a  piece  of  ice  ? 
How  much  latent  heat  does  water  contain  ? 
Is  the  real  zero  known  to  exist  ? 
How  can  ice  be  made  in  the  summer  ? 
Why  does  the  slaking  of  lime  produce  heat  ? 


QUESTIONS. 

CONVERSATION  V. 

What  kind  of  body  is  electricity  ? 

How  many  metals  are  required  to  produce  the  galvanic  action  ? 

Can  galvanism  be  produced  without  water  ? 

How  many  kinds  of  electricity  are  there  ? 

What  were  the  ideas  of  Dr.  Franklin  on  this  subject  ? 

What  is  said  to  produce  the  heat  of  the  electric  fluid  ? 

What  is  the  difference  between  electricity  and  galvanism  9 

What  difference  does  it  make  in  the  action  of  the  galvanic  bat- 
tery, whether  you  increase  the  number  of  plates,  or  enlarge 
their  dimensions  ? 

CONVERSATION  VI. 

Of  what  is  the  atmosphere  composed  ? 

What  is  a  gas  ? 

To  what  do  the  gases  owe  their  elasticity  ? 

What  proportions  of  oxygen  and  nitrogen  constitute  common 
air  ? 

When  a  substance  burns,  what  does  it  absorb  ? 

Why  is  it  necessary  to  heat  a  combustible  substance  to  make 
it  burn  ? 

Why  does  a  candle  confined  in  a  small  portion  of  air  soon  go 
out  ? 

How  does  oxygenatien  differ  from  combustion  ? 

Why  is  there  no  smoke  when  the  fire  burns  best  ? 

Do  the  constituents  of  the  atmosphere  exist  in  a  state  of  chem- 
ical combination  ? 

CONVERSATION  VII. 

What  does  the  word  hydrogen  signify  ? 

How  does  hydrogen  produce  water  ? 

Of  what  is  water  composed  ? 

What  are  the  means  of  decomposing  water  ? 

What  the  results  of  galvanic  action  upon  water? 

How  much  !  ghter  is  hydrogen  than  common  air? 

Will  oxygen  and^.yuiugeii  combine  in   any   other  proportion 

than  that  which  forms  wate;1  ? 
In  the  burning  of  a  candle,  why  is  there  a  little  space  of  wick, 

left  between  the  tallow  and  ti;?  oe  ? 
What  is  the  gas  called  which  is  used  in  lighting  streets  ? 
How  is  this  gas  procured  ? 


334  QUESTIONS. 

Describe  the  miner's  lamp. 
What  is  the  use  of  this  lamp  ? 

CONVERSATION  VIII. 

Where  is  sulphur  obtained  J 

How  does  brimstone  differ  from  ihejlowers  of  sulphur  ? 

What  is  sublimation  ? 

When  sulphur  is  burned/Vhat  is  the  product  ? 

From  whence  is  phosphorus  obtained  ? 

What  is  the  result  of  its  combustion  ! 

How  are  the  phosphorus  and  phosphoric  acid  formed  ? 

Does  phosphoric  combine  with  hydrogen  ? 

What  are  the  singular  properties  of  phosphuret  of  lime  ? 

CONVERSATION  IX. 

What  is  carbon  7 

Under  what  form  does  crystallised  charcoal  appear  ? 

Why  does  charcoal  burn  without  a  blaze  ? 

What  becomes  of  carbon  during  its  combustion  ? 

Is  it  possible  to  burn  a  diamond  ? 

What  is  the  product  of  its  combustion  ? 

Does  carbon  unite  with  more  than  one  proportion   of  oxygen  '.' 

Is  it  safe  to  breathe  carbonic  acid  ? 

Why  does  a  small  quantity  of  water  increase  the  flame  of  a 
fire  ? 

What  is  the  composition  of  black  lead? 

How  may  the  adulteration  of  volatile  oil  be  detected  ? 

What  are  the  products  of  a  burning  candle  or  lamp  ? 

How  does  carbon  restore  oxydated  substances  to  their  combus- 
tible state  ? 

CONVERSATION  X. 

How  many  metals  are  there  ? 

Name  them. 

Where  are  the  metals  found  r 

How  are  they  refined  ? 

Are  all  the  metals  combustible  r 

What  are  oxides  ? 

What  use  is  made  of  metallic  oxides  ? 

How  is  the  most  intense  heat  produced  ? 

Do  the  metals  oxydate  on  being  exposed  to  the  air  ? 

When  a  metal  dissolves  in  an  acid,  what  causes  the  heat  ? 


QUESTIONS.  335 

What  state  must  a  metal  be  in  before  it  can  be  dissolved  by  an 
acid  ? 

What  is  crystallization  ? 

Do  any  of  the  metals  combine  with  so  much  oxygen  as  to  be- 
come acids  ? 

At  what  degree  of  cold  does  mercury  become  solid  ? 

From  whence  do  the  metallic  oxides  derive  their  poisonous 
qualities  ? 

What  peculiarities  have  the  new  metals,  discovered  by  Sir  H. 
Davy  ? 

CONVERSATION  XIII. 

What  is  the  attraction  of  composition  ? 

What  is  the  kind  of  attraction  which  brings  acids  and  alkalies 
to  unite  '? 

What  are  the  seven  laws  of  chemical  attraction  ? 

What  are  the  salijiable  bases  ? 

What  are  the  salifiable  principles  ? 

How  do  salts  ending  in  ate  differ  from  those  ending  in  ite? 

How  do  acids  ending  in  ic  differ  from  those  ending  in  ous? 

How  are  chemical  compositions,  and  decompositions  effected  ? 

What  is  meant  by  quiescent,  and  diveilant  forces  ? 

When  acids  and  alkalies  unite  in  several  proportions,  what  rela- 
tion do  these  proportions  bear  to  each  other  ? 

When  a  salt  is  decomposed  by  galvanism,  at  which  pole  does 
the  acid  appear  ? 

CONVERSATION  XIV. 

What  are  the  alkalies  ? 
What  is  their  composition  ? 
What  are  the  general  properties  of  the  alkalies  ? 
On  what  does  the  causticity  of  the  alkalies  depend  9 
To  what  colour  do  the  alkalies  change  the  vegetable  blues  ? 
From  whence  is  potash  obtained  ? 
What  is  the  chemical  name  of  potash? 
What  is  its  composition  ? 

Why  is  heat  disengaged  when  water  is  poured  on  caustic  pot- 
ash ? 

What  is  the  result  when  potash  is  melted  with  silex  ? 
What  is  the  chemical  name  of  salt  petre  ? 
What  is  its  composition  ? 
From  whence  does  soda  derive  its  name  -? 
How  is  it  obtained  ? 


336  QUESTIONS. 

How  does  soda  differ  from  potash? 

Why  is  the  volatile  alkali  called  ammonia  ? 

From  what  is  it  extracted  ? 

By  what  means  can  ammonia  be  separated  from   the 

acid? 

Under  what  form  does  it  appear  when  pure  ? 
What  is  the  composition  of  ammonia  ? 
How  can  anmiouiacal  gas  be  retained  for  experiments  without  a 

mercurial  bath  f 
How  do  you  account  for  the  production  of  cold,   when   ice  is 

melted  with  amraoniacal  gas  ? 
What  is  the  substance  used  in   smelling  bottles,  called  harts 

horn  ? 

What  is  formed  when  ammonia  unites  with  oil  ? 
From  what  class  of  substances  can  ammonia  be  extracted  ? 

CONVERSATION    XV. 

What  is  the  number  of  earths,  and  what  their  names  ? 

Why  are  they  incombustible  ? 

W licit  costly  substances  do  the  earths  compose  ? 

Witti  what  are  the  gems  coloured  ? 

Which  a iv  the  alkaline  earths  ? 

Wiiat  substances  contain  silica  in  the  greatest  abundance  ? 

Wilit  is  the  composition  of  Derbyshire  spar? 

What  are  the  important  uses  of  silex  ? 

From  whence  does  alumine  derive  its  name  ? 

From  what  substance  is  this  earth  obtained  ? 

In  what  kind  of  soil  does  it  occur  most  abundantly  ? 

Is  it  useful  in  the  arts,  or  otherwise,  and  for  what  purposes  ' 

Name  the  alkaline  earths. 

Of  what  use  is  barytes  ? 

Has  it  any  remarkable  properties  ? 

In  what  respect  does  caustic  lime  differ  from  lime-stone  ? 

What  is  the  process  of  making  quick-lime? 

What  effect  does  the  air  produce  on  quick-lime  ? 

What  effect  has  water  on  it  ? 

What  is  the  cause  of  the   heat,  when  lime  is   sprinkled   with 

water  ' 

Does  it  dissolve  in  water,  and  in  what  proportion  ? 
What  is  the  process  of  making  lime-water  ? 
For  what  has  lime  a  remarkable  affinity  ? 
Why  does  lime-water  turn  white  on  breathing  into  U  ? 
Of  what  use  is  lime  in  the  arts  ? 
Of  what  use  is  it  in  agriculture  ? 


QUESTIONS.  337 

What  are  the  principal  uses  of  magnesia  ? 

Does  it  attract  water  ? 

In  what  state  is  it  used  in  medicine  ? 

What  does  it  form  when  combined  with  sulphuric  acid'.' 

Is  strontion  of  any  use  ? 

What  are  its  peculiarities  ? 

CONVERSATION  XVI. 

What  is  an  acid  ? 

What  are  the  general  properties  of  tire  acids  ? 

What  is  meant  by  the  radical  of  an  aci  J  ? 

What  substance  unites  to  the  radical  to  form  an  acid  ? 

How  does  the  language  of  chemistry   distinguish   the  stronger 

from  the  weaker  acid  ? 

What  term  is  used  to  denote  the  first  degree  of  oxygenation  ? 
When  a  radical  unites  with  another  proportion  of  oxygen  alter 

that  denoted  by  zc,  what  term  is  used  ? 
Vre  all  the  acids  capable  of  equal  degrees  of  oxygenation  ? 
What  is  the  number  of  acids  ? 
Plow  many  kinds  of  acids  are  there  ? 
Name  the  acids  which  are  known  to  have  simple  bases. 
Which  are  called  mineral  acids  ? 

Of  what  are  the  radicals  of  the  vegetable  acids  composed  ? 
Why  do  these  acids  differ,  when  composed  of  the  same  radicals  '{ 
What  are  the  names  of  the  vegetable  acids  ? 
Name  the  acids  with  triple  radicals. 

What  is  their  composition,  and  from  whence  are  they  obtained  ? 
By  what  means  can  the  acids  of  simple  radicals  be  decomposed  r 
Why  does  sulphuric  acid  change  the  colour  of  wood  to  black  ? 
Why  do  not  the  vegetable  acids  produce  the  same  effect  ? 
What  is  the  reason  fche  vegetable  acids  are  not  decomposed  by 

combustibles  ? 
Do  the  mineral  acids  have  the  same  effect  upon  the  skin  thai: 

they  do  on  wood  ?     If  they  do  not  what  is  the  reason  ? 

CONVERSATION  XVII 

What  is  the  chemical  name  of  oil  of  vitriol?. 
What  is  the  colour  and  smell  of  sulph.  acid  ? 
What  is  its  specific  gravity  ? 
What  is  the  consequence  of  mixing  it  with  water  .' 
What  is  the  process  for  obtaining  snip,  acid  ? 
What  the  best  antidote,  when  a  quantity  is  swallowed? 
How  can  the  sulphuric  acid  be  changed  to  the  sulphuro?/s  ^ 

30 


338 

What  use  is  ma3e  of  sulphurous  acid  ? 

What  is  the  easiest  process  for  making  this  acid  1 

Define  what  the  term  salt  means.' 

What  is  the  chemical  name  and  composition  of  Glaubers  salt? 

How  can  sulphate  of  soda  be  formed  ? 

What  qualities  in  the  salts  are  denoted  by  the  terms  efflorescent 

and  deliquescent? 

From  whence  comes  sulph.  ofalumine? 
What  are  its  principal  uses  ? 

How  is  sulphate  of  iron  manufactured  in  the  large  way  r 
What  substance  strikes  a  black  colour  with  sulph.  of  iron  ? 
Why  does  the  cutting  of  an  apple  turn  the  blade  of  the  knife 

black  ? 
Where  is  phosphate  of  lime  chiefly  found  ? 

CONVERSATION  XVIII. 

What  acids  are  formed  by  the  combination  of  nitrogen  and  ox- 
ygen ? 

What  acid  contains  the  greatest  proportion  of  oxygen  ? 

Explain  the  reason  why  nitric  acid  inflames  charcoal,  ol.  tur- 
pentine, &c. 

How  is  nitric  acid  obtained,  and  from  what  substance  ? 

How  can  nitric,  be  converted  in  nitrows,  acid ;  and  what  is  the 
cause  of  the  change  1 

Why  does  nitric  acid  act  with  peculiar  energy  on  combustibles  1 

How  can  nitrous  air  be  procured  from  nitric  acid,  and  what  is 
the  principle  ? 

How  is  nitrous  air  converted  into  nitrons  acid  gas  ? 

On  what  principle  can  nitrous  air  be  applied  to  test  the  purity 
of  the  atmosphere  ?     What  is  the  process  ? 

How  is  the  exhilarating  gas  procured  ? 

Describe  the  process  of  making  nitrate  of  ammonia. 

What  caution  is  necessary  before  it  is  breathed  ? 

When  do  chemical  decompositions  and  combinations  take  place 
during  the  formation  of  this  gas  from  nitrate  of  ammonia  ? 

Why  is  nitrate  of  potash  used  in  making  gun  powder,  rather 
than  any  other  salt  ? 

What  causes  the  detonation  when  gun  powder  is  fired  ? 

What  gas  is  formed  when  charcoal  is  burned  in  oxygen  gas  ? 

By  what  method  can  charcoal  be  procured  from  carbonic  acid  ? 

What  portion  of  the  atmosphere  is  formed  of  this  gas? 

By  what  means  is  this  gas  procured  for  experiment  ? 

From  whence  came  the  immense  quantity  of  carbonic  acid  con- 
tained in  limestone  rocks  ? 


QUESTIONS. 

In  what  manner  does  this  gas  destroy  life? 

W.iat  effect  does  it  have  on  vegetation  ? 

Wnat  are  the  waters  called  which  contain  this  gas  ? 

What  are  the  salts  called   which  are  partly  composed  of  this 

gas  / 
How  extensive  is  this  class  of  salts,  and  under  what  forms  do 

they  chiefly  occur  in  nature  ? 

CONVERSATION  XIX. 

What  is  the  basis  of  boracic  acid  ? 

What  is  the  composition  of  borax  ? 

What  are  its  uses  ? 

From  whence  \sfluoric  acid  obtained  ? 

What  are  its  peculiar  properties  ? 

Describe  the  method  of  etching  on  glass. 

With  what  is  muriatic  acid  chiefly  found  combined  ? 

What  is  the  natural  state  in  which  this  exists  ? 

How  can  this  gas  be  confined  without  a  mercurial  bath  ? 

What  is  the  basis  of  muriatic  acid  ? 

Is  this  acid  capable  of  combining  with  different  proportions  of 

oxygen  1 
Why  is  not  the  least  degree  of  oxygenation  called  the  muriat- 

ou.s  acid  ? 

How  is  oxy-muriatic  acid  obtained  ? 
Explain  the  reason  why  metals  inflame  in  this  gas. 
Why  does  a  mixture  of  nitric,  and  muriatic  acids  dissolve  gold, 

when  neither  of  them  will  do  it  alone  ? 
Why  does  oxy-muriatic  acid  turn  the   colour  of  vegetables 

white  1 

Of  what  use  is  this  acid  in  the  arts  ? 
Why  is  oxy-muriatic  acid  lately  called  chlorine  ? 
What  are  the  reasons  for  supposing  that  chlorine  is  a  simple 

substance  ? 

What  are  the  reasons  for  supposing  that  it  is  not  a  simple  sub- 
stance ? 

From  whence,  and  by  what  process  is  muriate  of  soda  obtained  ? 
What  two  gases,  when  mixed  form  muriate  of  ammonia?     De*- 

scribe  the  experiment. 

What  are  the  peculiar  properties  of  oxy-muriate  of  potash  ? 
Why  does  it  explode  on  being  rubbed  with  charcoal,  sulphur,  &c. 
What  gases  are  generated  at  the  moment  of  explosion  with 

charcoal  ?     Explain  the  changes  which  take  place,  and  thfc 

cause  of  the  detonation. 


aUESTlONS. 

How  can  phosphorus  be  set  on  fire  at  the  bottom  of  a  vessel  oi 

water  ?  and  how  do  you  account  for  it  ? 
What  are  the  peculiarities  ofiddinc  ? 
How  can  you  show  the  violet  coloured  gas  ? 
From  whence  is  iodine  obtained  ? 
"Why  is  it  considered  a  simple  body  ? 

CONVERSATION  XX. 

What  are  organised  bodies,  and  how  do  they  difter  from  inor- 
ganic matter  ? 

Define  what  life  is. 

What  constitutes  the  simplest  class  of  organised  bodies  ? 

Of  what  are  vegetables  chiefly  composed  ? 

What  are  the  materials  of  vegetables  ? 

Is  any  part  of  a  plant  composed  of  a  single  ingredient  ? 

Why  do  vegetables  decompose,  when  the  principle  of  life  is  ex- 
tinguished ? 

Vegetables  are  susceptible  of  two  kinds  of  analysis,  what  is  the 
object  of  each  ? 

What  is  mucilage,  and  what  are  its  uses  ? 

Can  gum  be  used  as  food  ? 

What  proportion  of  vegetables  contain  sugar? 

In  what  manner  is  sugar  obtained  from  the  sugar  cane  ? 

How  does  honey  differ  from  sugar  ? 

What  hfecula  ? 

What  is  gluten  ? 

How  many  kinds  of  vegetable  oils  are  there  ? 

From  what  part  of  plants  are  fixed  oils  obtained  r 

What  are  the  principal  drying  oils  ? 

On  what  does  this  quality  depend  ? 

Why  do  painters  a«ld  oxyd  of  lead  to  their  oils  ? 

To  what  is  the  rancidity  of  oil  owing  r 

Is  there  any  known  method  of  making  oil  by  combining  itfe 
principles  ? 

How  do  volatile  differ  horn  fixed  oils  ? 

How  are  volatile  oils  obtained  ? 

When  they  are  adulterated  with  fixed  oils  how  can  the  fraud  be 
detected  ? 

From  whence  does  camphor  come,  and  from  what  is  it  ex- 
tracted ? 

What  is  the  method  of  obtaining  it  ? 

Is  camphor  contained  in  other  plants  r 

What  are  resins  ? 

How  are  varnishes  prepared  r 


What  are  gum-resins  ? 

What  are  balsams  ? 

Give  some  account  of  caoutchouc  or  gum-elastic 

What  is  extractive  matter  ? 

What  is  the  condition  required  to  form  a  good  dye  ? 

Explain  the  nature  and  uses  of  mordants. 

What  substances  are  commonly  used  as  mordants  ? 

What  is  tannin  ? 

How  is  artificial  tannin  made  ? 

What  is  woody  fibre  ? 

Of  what  is  it  chiefly  composed  ? 

What  are  the  names  of  the  vegetable  acids  ? 

What  is  the  composition  of  the  bases  of  these  acids  ? 

What  is  the  gallic  acid  ? 

What  are  galls,  and  how  are  they  formed  ? 

How  does  the  oxalic  acid  remove  ink  spots  ? 

CONVERSATION  XXI. 

What  are  the  elements  into  which   vegetables  are  reduced  by 

natural  decomposition  ? 
What  is  the  process  called  which  disunites  and  decomposes  the 

elements  of  vegetables  ? 
How  many  kinds  of  fermentation  are  there  ? 
What  circumstances  are  necessary  to  induce  this  process  ? 
Give  some  account  of  the  saccharine  fermentation. 
What  is  the  process  of  making  malt  ? 
What  changes  do  the  ingredients  of  the  barley  undergo  to  form 

malt  ? 

What  is  the  second  fermentation  called  ? 
Why  does  barley  resist  the  vinous  fermentation  until  it  has 

gone  through  the  saccharine? 
What  changes  take  place  among  the  ingredients  present,  during 

the  vinous  fermentation  ? 

What  is  the  principal  difference  between  alcohol  and  sugar  ^ 
When  wine  is  distilled,  what  is  the  product  ? 
How  does  sugar  differ  from  starch? 
What  difference  is  there  between  gin  and  brandy  ? 
What  is  the  origin  of  cream  of  tartar  ? 
On  what  does  the  intoxicating  quality  of  liquors  depend? 
What  is  the  composition  of  alcohol? 
Describe  the  spirit  lamp. 
How  is  ether  obtained  ? 
How  does  it  differ  from  alcohol  ? 
What  is  the  effect  of  the  acetous  fermentation  r* 

30* 


342  QUESTIONS. 

What  is  the  reason  that  wine,  or  cider,  when  corked  tight  doe: 

not  turn  to  vinegar  ? 
What  kind  of  fermentation  is  excited  by  the  yeast  to  make 

bread  ? 
What  is  the  final  operation  of  nature  to  reduce  vegetables  to 

their  elements  ? 

How  are  petrifactions  formed  ? 
What  are  bitumens,  and  how  are  they  formed  1 
Why  does  naptha  preserve  potassium  ? 
What  is  asphaltum  ? 

What  is  coal,  and  what  are  its  ingredients  ? 
How  does  coke  differ  from  coal  ? 
What  is  amber,  and  where  is  it  found  ? 

CONVERSATION  XXII. 

From  whence  do  all  animals  ultimately  derive  their  sustenance? 

From  whence  do  plants  derive  their  food  ? 

W'ill  plants  live  on  pure  water? 

Why  do  animal  substances  make  the  best  manure"? 

What  part  of  the  seed  are  the  cotyledons  ? 

What  is  the  radicle  ?     What  is  the  plumule'? 

What  purpose  do  each  of  these  answer  during  germination  ? 

What  office  do  the  leaves  of  plants  perform  during  their  growth  ? 

What  different  functions  do  the  two  sides  of  the  leaves  per- 
form ? 

What  is  essential  to  the  developement  of  the  colours  of  plants? 

Why  is  air  necessary  to  the  growth  of  plants  ? 

In  what  way  does  animal  and  vegetable  life  mutually  support 
each  other? 

Through  what  vessels  does  the  sap  of  plants  ascend  ? 

What  is  the  distinction  between  aburnum,  and  heart-wood? 

How  is  pitch,  tar,  and  turpentine  obtained  ? 

Why  do  vegetables  grow,  only  during  the  warm  season  ? 

CONVERSATION  XXIII. 

What  are  the  fundamental  principles  of  animal  compounds  ? 
V*  hat  are  the  immediate  materials  of  animal  compounds  ? 
What  is  gelatine  1     What  use  is  made  of  it  in  the  arts,  or  in 

medicine  ? 

From  what  substance  is  gelatine  extracted  ? 
By  what  means  may  it  be  extracted  from  bones  ? 
Of  what  is  soup  composed  ? 
How  does  glue  differ  from  gelatine  ? 


.  aUESTIONS.  343 

What  is  albumen  ? 

Why  is  silver  tarnished  by  the  white  of  an  egg  P 

What  is  fibrine  ? 

How  may  it  be  procured  ? 

In  what  respect  does  the  composition  of  animal  oil,  differ  from 

the  oil  of  vegetables  l. 
What  are  the  bases  of  the  animal  acids  ? 
What  are  the  names  of  those  which  are  found  ready  formed  in 

animal  substances  1 

What  animal  acids  are  produced  by  decomposition  ? 
By  what  means  is  the  prussic  acid  procured  ? 
Does  this  acid  exist  ready  formed  in  blood  ? 
By  what  chemical  combinations  is  it  produced  1 
How  is  it,  that  this  colourless  acid  is  the  colouring  matter  of 

prussian  blue  ? 

What  is  carmine  ?     How  is  it  prepared  ?. 
WThat  is  ivory  black  1 

CONVERSATION  XXIV. 

What  is  animalisation? 

What  is  nutrition  ? 

What  are  the  principal  organs  by  which  the  operations  of  the 

animal  system  is  performed  ? 
What  are  the  ingredients  of  the  bones  ? 
From  whence  do  infants  obtain  phosphat  of  lime  ? 
How  are  the  teeth  formed  ? 
Under  what  circumstance  is  the  phosphate  of  lime  assimilated 

in  adult  animals? 

What  causes  the  disease  in  infants,  called  the  rickets  ? 
How  are  the  bones  connected  together  ? 
What  are  the  uses  of  the  cartilages  ? 
What  are  the  muscles  ? 

Where  are  they  situated,  and  what  are  their  uses  ? 
What  part  in  the  circulation  of  the  blood  does  the  arteries  per 

form  ? 

What  part  do  the  veins  perform  ? 
What  is  the  nature  of  the  lympht 
W  hat  is  chyle  ? 
What  is  its  use  ? 

What  is  the  composition  of  milk  ? 
What  functions  do  the  glands  perform  ? 
Does  the  blood  contain  all  the  substances  found  in  the  products 

of  secretion  1 
What  offices  do  the  nerves  perform  ? 


344  QUESTIONS. 

What  is  the  source  of  the  nervous  system  ? 

What  parts  of  the  animal  system  are  without  nerves  ?" 

How  is  it  that  the   nerves  convey  different  sensations,   when 

they  all  have  a  common  source? 
Of  how  many  coats  is  the  skin  comprised  r 
What  are  they  called  ? 
Where  is  the  colour  of  the  skin  situated  ? 
What  difference  in  colour  is  there  between   the  cuticle  of  a 

white  man,  and  a  black  one? 

CONVERSATION  XXV. 

What  is  digestion  ? 

Where  is  it  performed  ? 

What  is  the  solvent  of  the  food  in  the  stomach  ? 

Are  the   coats  of  the  stomach  liable  to  be  destroyed  by  the 

gastric  juice  ? 

What  produces  the  sensation  of  hunger  ? 
What  is  the  aliment  called  after  it  has  been   acted  on  by  the 

gastric  juice  ? 

What  changes  does  the  chyme  undergo  before  it  is  absorbed  ? 
By  what  system  of  vessels  is  the  chyle  taken  up  ? 
How  does  it  obtain  admittance  into  circulation  ? 
In  what  does  respiration  consist  ? 
What  constitutes  the  mechanical  part  of  this  process  1 
By  what  means  is  the  ch$si  expanded  so  as  to  admit  air  into 

the  lungs  ? 

How  many  times  does  a  person  breathe  in  a  minute  ? 
Describe  the  circulation  of  the  blood. 
How  does  arterial  blood  differ  from  venous  1 
How  do  you  account  for  the  difference  of  colour  between  them  ? 
What  are  the  two  cavities  of  the  heart  called  ? 
Which  cavity  receives  the  arterial,  and  which  the  venous  blood  ? 
W'hat  change  does  the  blood  undergo  in  its  passage  through 

the  lungs  t 

What  effect  does  respiration  have  on  the  air  we  breathe? 
The  blood  undergoes  two  circulations  ;   what  is  the  difference 

between  them  ? 
What  is  the  quantity  of  carbon  expelled  from  the  lungs  of  a 

person  in  24  hours  ? 

What  quantity  of  air  do  we  take  into  our  lungs  at  each  inspira- 
tion ' 
Is  it  absolutely  certain  that  the  carbon  emitted  by  respiration 

comes  from  the  blood 
Are  all  the  products  of  secretion  contained  in  the  blood  P 


QUESTIONS.  345 

If  not,  how  is  it  most  probable  that  these  new  substances  are 

formed  ? 
By  what  system  of  vessels  is  the  perspiration  secreted  ? 

CONVERSATION  XXVI. 

What  analogy  is  there  between  the  effects  of  respiration,  and 
thjjse  of  combustion  ? 

What  is  the  principal  source  of  animal  heat  ? 

What  are  the  objections  to  Black's  theory  of  animal  heat  ? 

How  are  these  objections  obviated  ? 

What  objections  can  be  brought  against  Dr.  Crawford's  theory*? 

What  does  Mr.  Brodie's  experiment  prove  ? 

What  are  the  objections  to  Dr.  Cooper's  theory  ? 

W7hat  are  the  objections  against  Dr.  Philip's  theory  ? 

Why  is  the  heat  increased  duripg  a  fever  ? 

Why  does  not  violent  exercise  greatly  increase  the  temperature 
of  the  body  1 

On  what  principle  is  it  that  the  temperature  of  the  body  remains 
the  same  in  winter  as  in  summer  ? 

Is  the  temperature  of  a  living  animal  raised  by  being  exposed 
to  a  heat,  greater  than  that  of  its  own  body  ? 

How* is  it  proved  that  fish  cannot  live  without  air? 

What  effect  does  the  respiration  of  a  large  or  small  quantity 
of  air  have  on  the  muscular  powers  of  animals  ? 

Why  are  amphibious  animals  enabled  to  remain  a  long  time 
under  water  1 

What  is  composition  of  milk? 

What  are  the  ingredients  in  milk? 

What  does  cream  absorb  from  the  atmosphere  to  turn  it  into 
butter? 

Why  does  the  butter-milk  become  sour  when  the  butter  separa- 
ted from  it  is  sweet  ? 

What  causes  butter  to  become  rancid  ? 

What  does  rennet  contain  which  causes  the  coagulation  of  milk? 

What  is  spermaceti  ? 

What  is  ambergris'? 

By  what  process  does  dead  animal  matter  return  to  its  elemen- 
tary state  ? 


A  VOCABULARY 

OF 

CHEMICAL  TERMS. 


A. 

Acetates.  Compounds  formed  by  the  combination  of  a  base 
with  acetic  acid. 

Adds.  Compounds  formed  by  the  combination  of  oxygen 
with  certain  elementary  bodies  forming  in  general  a  class  ot 
substances,  which  are  sour  to  the  taste,  and  which  unite  with 
alkalies,  and  metallic  oxides  to  form  salts. 

Acidules.  Substances  formed  by  the  natural  combination  of 
some  acids  with  a  quantity  of  potash.  The  oxalic  and  tar- 
taric  acids  are  examples. 

Aeriform  fluids.  Elastic  fluids.  Atmospheric  air,  and  the 
gases  are  of  this  kind.  Their  aeiform  state  is  owing  to  the 
caloric  with  which  their  bases  are  combined. 

Affinity,  chemical.  A  term  used  to  express  that  peculiar  pro- 
pensity which  substances  of  different  kinds  have  to  unite  with 
each  other,  as  acids  and  alkalies,  &c. 

— —  of  aggregation.  That  force  is  so  called  by  which  sub- 
stances of  the  same  kind  tend  to  unite,  without  changing  their 
qualities. 

— —  of  composition.  That  force  by  which  substances  of 
different  kinds  combine,  and  form  a  third,  which  differs  from 
either  of  the  two  first,  before  the  combination.  Thus  muri- 
atic acid  and  soda  form  common  salt. 

Albumen.  Coagulable  lymph.  It  is  contained  in  animal  sub- 
stances, as  the  serum  of  the  blood.  The  white  of  eggs  is  al- 
bumen. 

Alcohol.  Rectified  spirit  of  wine.  It  is  always  the  same,  from 
whatever  kind  of  spirit  it  is  distilled. 

Alkalies.  Peculiar  substances  which  have  a  caustic  burning 
taste,  and  a  strong  tendency  to  combination,  particularly 
with  acids,  and  witjh  water. 


A  VOCABULARY  OF  CHEMICAL  TERMS.         347 

Alloys.     A  combination  of  any  two  metals,  except  mercury. 

Brass  is  an  alloy  of  copper  and  zinc. 
Amalgam.     A  mixture  of  mercury  with  any  other  metal. 
Analysis.     Separation  of  the  constituent  parts  of  compounds, 

for  the  purpose  of  detecting  their  composition.     This  is  done 

by  reagents. 
Annealing.     Rendering  substances  tough,  which  before  were 

brittle.     The  metals  are  annealed  by  heating  them  red  hot, 

and  then  cooling  them  gradually. 
Arscniates.     Salts}  formed  by  the  combination  of  a  base  with 

the  arsenic  acid. 

Azote.  This  name  is  given  by  the  French  chemists  to  nitro- 
gen, which  see. 

B. 

Balsams.     Resinous,  semi-fluid  substances,  which  are  obtained 

from  certain  trees  by  making  incisions. 
Barometer.     An  instrument  which  indicates  the  variations  of 

the  pressure  of  the  atmosphere,  as  thermometers  do  of  heat 

and  cold. 
Base.     A  term  used  by  chemists  to  denote  the  substance  to 

which  an  acid  is  united  to    form  a  salt.     Thus  soda  is  the 

base  of  common  salt. 
Benzoates.     Salts  formed  by  the  union  of  the  benzoic  acid  with 

a  base. 
Blow-Pipe.     An  instrument  to  increase  and  direct  the  flame  of 

a  lamp  for  the  analysis  of  minerals,  and  for  other  chemical 

purposes. 
Borates.     Salts  formed  by  the  combination  of  any  base  with 

the  acid  of  borax. 

c. 

Calcareous.  A  chemical  term  formerly  applied  to  describe* 
chalk,  marble,  and  all  other  combinations  of  lime  with  car- 
bonic acid. 

Calcination.  The  application  of  heat  to  saline,  metallic,  or 
other  substances  ;  so  regulated  as  to  deprive  them  of  mois- 
ture, &c.  and  yet  preserve  them  in  a  pulverulent  form. 

Caloric.     The  chemical  term  for  the  matter  of  heat. 

free.  Is  caloric  in  a  separate  state,  or,  if  attached  to- 
other substances,  not  chemically  united  with  them. 

latent.    Is  the  term  made  use  of  to  express  that  por- 


348  A    VOCABULARY 

tion  of  caloric  which  is  chemically  united  to  any  substance,, 
so  as  to  become  <\.part  of  the  said  substance. 

Calorimeter.  An  instrument  for  ascertaining  the  quantity  of 
caloric  disengaged  from  any  substance  that  may  be  the  ob- 
ject of  experiment. 

Calx.     An  old  term  made  use  of  to  describe  a  metallic   oxide. 

Camphor atas.  Salts  formed  by  the  combination  of  any  base 
with  the  camphoric  acid. 

Capillary.  A  term  usually  applied  to  the  rise  of  the  sap  in 
vegetables,  or  the  rise  of  any  fluid  in  very  small  tubes ;  owing 
to  a  peculiar  kind  of  attraction,  called  capillary  attraction. 

Carbon.     The  basis  of  charcoal. 

Carbonates.  Salts  formed  by  the  combination  of  any  base  with 
carbonic  acid. 

Carburets.  Compound  substances,  of  which  carbon  forms  om 
of  the  constituent  parts.  Thus  plumbago,  which  is  compo- 
sed of  carbon  and  iron,  is  called  carburet  of  iron. 

Causticity.  That  quality  in  certain  substances  by  which 
they  burn  or  corrode  animal  bodies  to  which  they  are  appli- 
ed. It  is  best  explained  by  the  doctrine  of  chemical  affinity. 

Chalybeate.  A  term  descriptive  of  those  mineral  waters  which 
are  impregnated  with  iron. 

CharcoaL  Wood  burnt  in  close  vessels :  it  is  an  oxide  of 
carbon,  and  generally  contains  a  small  portion  of  salts  and 
earth.  Its  carbonaceous  matter  may  be  converted  by  com- 
bustion into  carbonic  acid  gas. 

Chlorine.  A  name  lately  given  to  the  substance  usually  called 
oxymuriatic  acid.  Its  compounds  are  called  by  the  name  of 
their  bases  with  the  ending  of  anc.  As  phosphorane,  sul- 
phurane,  &c. 

Chromates.  Salts  formed  by  the  combination  of  any  bas* 
with  the  chromic  acid. 

Citrates.  Salts  formed  by  the  combination  of  any  base  with 
citric  acid. 

Coal.  A  term  applied  to  the  residuum  of  any  dry  distillation 
of  animal  or  vegetable  matters. 

Cohesion.  A  force  inherent  in  all  the  particles  of  all  substan- 
ces, excepting  light  and  caloric,  which  prevents  bodies  from 
falling  in  pieces. 

Columbates.  Salts  formed  by  the  combination  of  any  base  with 
the  columbic  acid. 

Combination.  A  term  expressive  of  a  true  chemical  union  of 
two  or  more  substances ;  in^opposition  to  mere  mechan- 
ical mixture. 

Combustibles.     Certain  substances  which  are  capable  of  con? 


OP    CHEMICAL    TERMS. 

tuning  more  or  less  rapidly  with  oxygen.  They  are  divided 
by  chemists  into  simple  and  compound  combustibles. 

(Combustion  The  act  of  absorption  of  oxygen  by  combustible 
bodies  from  atmospheric  or  vital  air.  The  word  decombus- 
tion  is  sometimes  used  by  the  French  writers  to  signify  the 
opposite  operation. 

Crucibles.  Vessels  of  indispensable  use  in  chemistry  in  the 
various  operations  of  fusion  by  heat.  They  are  made  of  ba- 
ked earth,  or  metal,  in  the  form  of  an  inverted  cone. 

Crystallization.  An  operation  of  nature,  in  which  various 
earths,  salts,  and  metallic  substances,  pass  from  a  fluid  to  a 
solid  state,  assuming  certain  determinate  geometrical  figures. 

-'  •  •  water  of.  That  portion  which  is  combined  with 

salts  in  the  act  of  crystallizing,  and  becomes  a  component  part 
of  the  said  saline  substances. 

Cupel.  A  vessel  made  of  calcined  bones,  mixed  with  a  small 
proportion  of  clay  and  water.  It  is  used  whenever  gold  and 
silver  are  refined  by  melting  them  with  lead.  The  process- 
is  called  cupellation. 

D. 

Decomposition.  The  separation  of  the  constituent  principles 
of  compound  bodies  by  chemical  means. 

Deflagration.  The  vivid  combustion  that  is  produced  whene- 
ver nitre,  mixed  with  an  inflammable  substance,  is  exposed 
to  a  red  heat.  It  may  be  attributed  to  the  extrication  of  ox- 
ygen from  the  nitre,  and  its  being  transferred  to  the  inflam- 
mable body  ;  as  any  of  the  nitrates  or  oxygenized  muriates 
will  produce  the  same  effect. 

Deliquescence  of  solid  saline  bodies,  signifies  their  becoming 
moist,  or  liquid,  by  means  of  water  which  they  absorb  from 
the  atmosphere  in  consequence  of  their  great  attraction  for 
that  fluid. 

Deoxidize  (formerly  deoxidate.)  To  deprive  a  body  of  oxygen. 

Deoxidizement.  A  term  made  use  of  to  express  that  operation 
by  which  one  substance  deprives  another  substance  of  its 
oxygen.  It  is  called  unburning  a  body  by  the  French  chem- 
ists. 

Detonation.  An  explosion  with  noise.  It  is  most  commonly 
applied  to  the  explosion  of  nitre  when  thrown  upon  heated 
charcoal. 

Digestion.     The  effect  produced  by  the  continued  soaking  of 
a  solid  substance  in  a  liquid,  with  the  application  of  heat 
3* 


A  VOCABULARY 

Papirfs.  An  apparatus  for  reducing  animal  or  vt- 
getable  substances  to  a  pulp  or  jelly  expeditiously. 

Distillation  A  process  for  separating  the  volatile  parts  of  a 
substance  from  the  more  fixed,  and  preserving  them  both  in 
a  state  of  separation. 

Ductility.  A  quality  of  certain  bodies,  in  consequence  of  which 
they  may  be  drawn  out  to  a  certain  length  without  fracture. 

'Didcification.  The  combination  of  mineral  acids  with  alcohol. 
Thus  we  have  dulcified  spirit  of  nitre,  dulcified  spirit  of  vit- 
riol, &c. 

E. 

EdulcQration.  Expressive  of  the  purification  of  a  substance  by 
washing  with  water. 

Effervescence.  An  intestine  motion  which  takes  place  in  cer- 
tain bodies,  occasioned  by  the  sudden  escape  of  a  gaseous 
substance. 

Efflorescence.  A  term  commonly  applied  to  those  saline  crys- 
tals which  become  pulverulent  on  exposure  to  the  air,  in  con- 
sequence of  the  loss  of  a  part  of  the  water  of  crystallization. 

Elasticity.  A.  force  in  bodies,  by  which  they  endeavour  to  re- 
store themselves  to  the  posture  from  whence  they  were  dis- 
placed by  an  external  force. 

Elastic  fluids.  A  name  sometimes  given  to  vapours  and  gas- 
es. Vapour  is  called  an  clastic  fluid  ;  gas,  a  permanently 
elastic  fluid. 

Elective  Attractions.  A  term  used  by  Bergman  and  others  to 
designate  what  we  now  express  by  the  words  chemical  affin- 
itij^  When  chemists  first  observed  the  power  which  one 
compound  substance  has  to  decompose  another,  it  was  ima- 
gined that  the  minute  particles  of  some  bodies  had  a  prefer- 
°nce  for  some  other  particular  bodies  5  hence  this  property  of 
matter  acquired  the  term  elective  attraction. 

Elements.  The  simple,  constituent  parts  of  bodies  which  are 
incapable  of  decomposition  ;  they  are  frequently  called  prin- 
ciples. 

Empyreuma.  A  peculiar  and  indescribably  disagreeable  smell, 
arising  from  the  burning  of  animal  and  vegetable  matter  in 
close  vessels. 

Ethers.  Volatile  liquids  formed  by  the  distillation  of  some  of 
the  acids  with  alcohol. 

Evaporation.  The  converson  of  fluids  into  vapour  by  heat. 
This  appears  to  be  nothing  more  than  a  gradual  solution  of 


OP    CHEMISAL    TERMS.  331 

the  aqueous  particles  in  atmospheric  air,  owing  to  the  chem- 
ical attraction  of  the  latter  for  water. 

Eudiometer.  An  instrument  invented  by  L)r.  Priestley  for  de- 
termining the  purity  of  any  given  portion  of  atmospheric  air. 
The  science  of  investigating  the  different  kinds  of  gases  i£ 
called  eudiometry. 

F. 

Fermentation.  A  peculiar  spontaneous  motion,  which  takes 
place  in  all  vegetable  matter  when  exposed  for  a  certain  time 
to  a  proper  degree  of  temperature. 

Fibrine.  That  white  fibrous  substance  which  is  left  after  free- 
ly washing  the  coagulum  of  the  blood,  and  which  chiefly 
composes  the  muscular  fibre. 

Flowers.  In  chemical  language,  are  solid  dry  substances  re- 
duced to  a  powder  by  sublimation.  Thus  we  have  flowers 
of  arsenic,  of  sal  ammoniac,  of  sulphur,  &c.  which  are  arsenic, 
sal  ammoniac,  and  sulphur  unaltered  except  in  appearance. 

Fluatcs.  Salts  formed  by  the  combination  of  any  base  with 
fluoric  acid. 

Fluidity.  A  term  applied  to  all  liquid  substances.  Solids  are 
converted  to  fluids  by  combining  with  a  certain  portion  of 
caloric. 

Flux.  A  substance  which  is  mixed  with  metallic  ore,  or  other 
bodies  to  promote  their  fusion  ;  as  an  alkali  is  mixed  with  si- 
lex,  in  order  to  form  glass. 

Fulmination.  Thundering  or  explosion  with  noise.  We  have 
fulminating  silver,  fulminating  gold,  and  other  fulminating 
powders,  which  explode  with  a  loud  report  by  friction,  or 
when  slightly  heated. 

Fusion.  The  state  of  ai)ody  which  was  solid  in  the  tempera- 
ture of  the  atmosphere,  and  is  now  rendered  fluid  by  the  ar- 
tificial application  of  heat. 

G. 

Gallates.  Salts  formed  by  the  combination  of  any  base  with 
gallic  acid. 

Ghlvanism.  A  new  science  which  oflfers  a  variety  of  phenome- 
na, resulting  from  different  conductors  of  electricity  placed  in 
different  circumstances  of  contact ;  particularly  the  nerve*  of 
the  animal  body. 

Gas.  All  solid  substances,  when  converted  into  permanently 
elastic  fluids  by  caloric,  are  called  gases, 


A  VOCABULARY 

Having  the  nature  and  properties  oi  gas. 

Gasometer.  A  name  given  to  a  variety  of  utensils  and  appara- 
tus contrived  to  measure,  collect,  preserve,  or  mix  the  differ- 
ent gases.  An  apparatus  of  this  kind  is  also  used  for  the 
purposes  of  administering  pneumatic  medicines. 

Gelatine.  A  chemical  term  for  animal  gelly.  It  exists  partic- 
ularly in  the  tendons  and  the  skin  of  animals. 

Gluten,  A  vegetable  substance  somewhat  similar  to  animal 
gelatine.  It  is  the  gluten  in  wheat  flour  which  gives  it  the 
property  of  making  good  bread,  and  adhesive  paste.  Other 
grain  contains  a  much  less  quantity  of  this  nutritious  sub- 
stance. 

Grain.  The  smallest  weight  made  use  of  by  chemical  writers. 
Twenty  grains  make  a  scruple  ;  3  scruples  a  drachm ;  8 
drachms,  or  480  grains,  make  an  ounce ;  12  ounces,  or  5760 
grains,  a  pound  troy.  The  avoirdupois  pound  contains  7009 
grains. 

Granulation.  The  operation  of  pouring  a  melted  metal  into 
water,  in  order  to  divide  it  into  small  particles  for  chemical 
purposes.  Tin  is  thus  granulated  by  the  dyers  before  it  is 
dissolved  in  the  proper  acid. 

Gravity,  specific.  This  differs  from  absolute  gravity  in  as 
much  as  it  is  the  weight  of  a  given  measure  of  any  solid  or 
fluid  body,  compared  with  the  same  measure  of  distilled  wa- 
ter. It  is  generally  expressed  by  decimals. 

Gums.  Mucilaginous  exudations  from  certain  trees.  Gum 
consists  of  lime,  carbon,  oxygen,  hydrogen,  and  nitrogen  with 
a  little  phosphoric  acid. 

H. 

Heat,  mutter  of.     See  Caloric. 

Hermetically.  A  term  applied  to  the  closing  of  the  orifice  of  a 
glass  tube,  so  as  to  render  it  air-tight.  Hermes,  or  Mercury, 
was  formerly  supposed  to  have  been  the  inventor  of  chemis- 
try :  hence  a  tube  which  was  closed  for  chemical  purposes, 
was  said  to  be  Hermetically  or  chemically  sealed.  It  is  usu- 
ally done  by  melting  the  end  of  the  tube  by  means  of  a  blow- 
pipe. 

Hydrogen.  A  simple  substance;  one  of  the  constituent  parts 
of  water. 

gas.  Solid  hydrogen  united  with  a  large  portion  of 

caloric.  It  is  the  lightest  of  all  the  known  gases.  Hence 
»t  is  used  to  inflate  balloons.  It  was  formerly  called  inflam- 
mable air. 


OP    CHEMICAL    TERMS. 


353 


Hydro-Carbonates.  Combinations  of  carbon  with  hydrogen 
are  described  by  this  term.  Hydro-carbonate  gas  is  procur- 
ed from  moistened  charcoal  by  distillation. 

Hydrogenized  sulphurets.  Certain  bases  combined  with  sul- 
phuretted hydrogen. 

Hydro-Oxides.     Metallic  oxides  combined  with  water. 

Hydrometers.  Instruments  for  ascertaining  the  specific  gravi- 
ty of  spiritous  liquors  or  other  fluids. 

Hygrometers  Instruments  for  ascertainiug  the  degree  of  mois- 
ture in  atmospheric  air. 

Hyperoxygenized.  A  term  applied  to  substances  which  are 
combined  with  the  largest  possible  quantity  of  oxygen.  We 
have  muriatic  acid,  oxygenized  muriatic  acid,  and  hyperoxy- 
genized  muriatic  acid.  The  latter  can  be  exhibited  only  in 
combination. 

I. 

Inflammation.  A  phenomenon  which  takes  place  on  mixing 
certain  substances.  The  mixture  of  oil  of  turpentine  with 
strong  nitrous  acid  is  an  instance  of  this  peculiar  chemical  ef- 
fect. 

Infusion.  A  simple  operation  to  procure  the  salts,  juices,  and 
other  virtues  of  vegetables  by  means  of  water. 

Intermediates.  A  term  made  use  of  when  speaking  of  chemic- 
al affinity.  Oil,  for  example,  has  no  affinity  for  water  unless 
it  be  previously  combined  with  an  alkali;  it  then  becomes 
soap,  and  the  alkali  is  said  to  be  the  intermedium  which  oc- 
casions the  union. 

K. 

Kali.  A  genus  of  marine  plants  which  is  burnt  to  procure  min- 
eral alkali  by  afterwards  lixiviating  the  ashes. 

L. 

Laboratory.  A  room  fitted  up  with  apparatus  for  the  per- 
formance of  chemical  operations 

Lactates.  Salts  formed  by  the  combination  of  any  base  with 
lactic  acid. 

Lakes.  Certain  colours  made  by  combining  the  colouring  mat- 
ter of  cochineal,  or  of  certain  vegetables,  with  pure  alumine, 
or  with  oxide  of  tin,  zinc,  &c. 

Lamp,  Argand's.  A  kind  of  lamp  much  used  for  chemical  ex- 

31* 


3  A    VOCABULAR\ 

periments.  It  is  made  on  the  principle  of  a  wind  furnace , 
and  thus  produces  a  great  degree  of  light  and  heat  withou  1 
smoke. 

Lens.  A  glass,  convex  on  both  sides,  for  concentrating  the 
rays  of  the  sun.  It  is  employed  by  chemists  in  fusing  re- 
fractory substances  which  cannot  be  operated  upon  by  an  or- 
dinary degree  of  heat- 

Levigation.  The  grinding  down  of  hard  substances  to  an  im- 
palpable powder  on  a  stone  with  a  muller,  or  in  a  mill  adapt- 
ed to  the  purpose. 

Litharge.  An  oxide  of  lead  which  appears  in  a  state  of  vitri- 
fication. It  is  formed  in  the  process  of  separating  silver 
from  lead. 

Lixiviation.  The  solution  of  an  alkali  or  a  salt  in  water,  or  in 
some  other  fluid,  in  order  to  form  a  lixivium. 

Lixivium.     A  fluid  impregnated  with  an  alkali  or  with  a  salt. 

Lute.  A  composition  for  closing  the  junctures  of  chemical  ves- 
sels to  prevent  the  escape  of  gas  or  vapour  in  distillation. 

M. 

Maceration.  The  steeping  of  a  solid  body  in  a  fluid  in  order 
to  soften  it,  without  impregnating  the  fluid. 

Malates.  Salts  formed  by  the  combination  of  any  base  with 
malic  acid. 

Malleability.  That  property  of  meta's  which  gives  them  the 
capacity  of  being  extended  and  flattened  by  hammering.  Il 
is  probably  occasioned  by  latent  caloric. 

Massicot.  A  name  given  to  the  yellow  oxide  of  lead,  as  minium 
is  applied  to  the  red  oxide. 

Matrass.     Another  name  for  a  bolt-head. 

Menstruum.  The  fluid  in  which  a  solid  body  is  dissolved. 
Thus  water  is  a  menstruum  for  salts,  gums,  &c.  and  spirit  oi 
wine  for  resins. 

Metallic  Oxides.  Metals  combined  with  oxygen.  By  this 
process  they  are  generally  reduced  to  a  pulverulent  form  ; 
are  changed  from  combustible  to  incombustible  substances  ; 
and  receive  the  property  of  being  soluble  in  acids. 

Mineral.  Any  natural  substance  of  a  metallic,  earthy,  or  sa- 
line nature,  whether  simple  or  compound,  is  deemed  a  mine- 
ral. 

Mineralizers.  Those  substances  which  are  combined  with 
metals  in  their  ores;  such  are  sulphur,  arsenic,  oxygen,  car- 
bonic acid,  &c. 

Mineralogy.    The  science  of  fossils  and  minerals- 


OF    CHEMICAL    TERMS.  355 

Mineral  Waters.  Waters  which  hold  some  metal,  earth,  or 
salt,  in  solution.  They  are  frequently  termed  Medicinal 
Waters. 

Molybdatcs.  Salts  formed  by  the  combination  of  any  base 
with  the  molybdic  acid. 

Mordants.  Substances  which  have  a  chemical  affinity  for  par- 
ticular colours ;  they  are  employed  by  dyers  as  a  bond  to 
unite  the  colour  with  the  cloth  intended  to  be  dyed.  Alum 
is  of  this  class. 

Mucilage.  A  glutinous  matter  obtained  from  vegetables,  trans- 
parent and  tasteless,  soluble  in  water,  but  not  in  spirit  of 
wine.  It  chiefly  consists  of  carbon  and  hydrogen,  with  a 
little  oxygen. 

Wucitcs.  Salts  formed  by  the  combination  of  any  base  with 
the  raucous  acid. 

Mitjlc.  A  semi-cylindrical  utensil,  resembling  the  tilt  of  a 
boat,  made  of  baked  clay  ;  its  use  is  that  of  a  cover  to  cu- 
pels in  the  assay  furnace,  to  prevent  the  charcoal  from  fall- 
ing upon  the  metal,  or  whatever  is  the  subject  of  experiment. 

Muriates.  Salts  formed  by  the  combination  of  any  base  with 
muriatic  acid. 


Natron.     One  of  the  names  for  mineral  alkali,  or  soda. 

'Neutralize.  When  two  or  more  substances  mutually  disguise 
each  other's  properties,  they  are  said  to  neutralize  one  anoth- 
er. 

~^etttr;t1  Salt.  A  substance  formed  by  the  union  of  an  acid 
with  an  alkali,  an  earth,  or  a  metallic  oxide,  in  such  propor- 
tions as  to  saturate  both  the  base  and  the  acid. 

Nitrates.  Salts  formed  by  the  combination  of  any  base  with 
nitric  acid. 

Nitrogen.  A  simple  substance,  by  the  French  chemists  called 
azote.  It  enters  into  a  variety  of  compounds,  and  forms 
more  than  three  parts  in  four  of  atmospheric  air. 

O. 

Ochres.  Various  combinations  of  the  earths  with  oxide,  or 
carbonate,  of  iron. 

Ores.  Metallic  earths,  which  frequently  contain  several  extra- 
neous matters ;  such  as  sulphur,  arsenic,  &c. 

Oxalatcs.  Salts  formed  by  the  combination  of  any  base  with 
oxalic  acid. 


356  A  VOCABULARY 

Oxide.  Any  substance  combined  with  oxygen,  in  a  proper* 
tion  not  sufficient  to  produce  acidity. 

Oxidize.  To  combine  oxygen  with  a  body  without  producing 
acidity. 

Oxidizemmt.  The  operation  by  which  any  substance  is  com- 
bined with  oxygen,  in  a  degree  not  sufficient  to  produce  acidity. 

Oxygen.  A  simple  substance  composing  the  greatest  part  of 
water,  and  part  of  atmospheric  air. 

— — gas.  Oxygen  converted  to  a  gaseous  state  by  calo- 
ric. It  is  also  called  vital  air.  It  forms  nearly  one-fourth 
of  atmospheric  air. 

Oxygenize.  To  acidify  a  substance  by  oxygen.  Synonymous 
with  Oxygenate  5  but  the  former  is  the  better  term. 

Oxygenizeme.nt.     The  production  of  acidity  by  oxygen. 

P. 

Pellicle.  A  thin  skin  which  forms  on  the  surface  of  saline  so- 
lutions and  other  liquors,  when  boiled  down  to  a  certain 
strength. 

Phlogiston.  An  old  chemical  name  for  an  imaginary  sub- 
stance, supposed  to  be  a  combination  of  fire  with  some  other 
matter,  and  a  constituent  part  of  all  inflanmiabJe  bodies,  and 
of  many  other  substances. 

Phosphates.  Salts  formed  by  the  combination  of  any  base 
with  phosphoric  acid. 

Phosphites.  Salts  formed  by  the  combination  of  any  base 
with  phosphorous  acid. 

Phosphurets.  Substances  formed  by  an  union  with  phospho- 
rus. Thus  we  have  phosphuret  of  lime,  phosphuretted  hy- 
drogen, &c. 

Plumbago.     Carburet  of  iron,  or  the  black  lead  of  commerce. 

Pneumatic.     Any  thing  relating  to  the  airs  and  g'ases. 

trough.     A  vessel  filled  in  part    with   water 

or  mercury,  for  the  purpose  of  collecting  gases,  so  that  they 
may  be  readily  removed  from  one  vessel  to  anoiiit  r. 

Precipitate.  Any  matter  which,  having  been  dissolved  in  a 
fluid,  falls  J;o  the  bottom  of  the  vessel  on  the  addition  of  some 
other  substance  capable  of  producing  a  decomposition  of  the 
compound,  in  consequence  of  its  attraction  either  for  the 
menstruum  or  for  the  matter  which  was  before  held  in  solu- 
tion. 

Precipitation.  That  chemical  process  by  which  bodies  dissol- 
ved, mixed,  or  suspended  in  a  fluid,  are  separated  from  that 
fluid,  and  made  to  gravitate  to  the  bottom  of  the  vessel. 


OF  CHEMICAL  TERMS.  357 

Prussiates.  Salts  formed  by  the  combination  of  any  base  with 
prussic  acid. 

rut  refaction.  The  last  fermentative  process  of  nature,  fry 
which  organized  bodies  are  decomposed  so  as  to  separate 
their  principles,  for  the  purpose  of  reuniting  them  by  future 
attractions,  in  the  production  of  new  compositions. 

Pyrites.  An  abundant  mineral  found  on  the  English  coasts, 
and  elsewhere.  Some  are  sulphurets  of  iron,  and  others 
sulphurets  of  copper,  with  a  portion  of  alum  me  and  silex. 
The  former  are  worked  for  the  sake  of  the  sulphur,  and  the 
latter  for  sulphur  and  copper.  They  are  also  called  Mar- 
casites  and  Fire-stone. 

martial.  That  species  of  pyrites  which  contains 

iron  for  its  basis.  See  a  full  accouut  of  these  minerals  in 
HenckePs  Pyritologia. 

Pyrometer.  An  instrument  invented  by  Mr.  Wedgwood  for 
ascertaining  the  degrees  of  heat  in  furnaces  and  intense  fires. 
See  Philosophical  transactions,  vol.  Ixii.  and  Ixiv.  and  Chem- 
ical Catech. 

Pyrophori.  Compound  substances  which  heat  of  themselves, 
and  take  fire  on  the  admission  of  atmospheric  air.  See  an 
account  of  a  variety  of  experiments  with  these  composi- 
tions in  Wiegleb's  Chemistry,  quarto,  page  622,  &c. 

Q. 

Quartz.  A  name  given  to  a  variety  of  siliceous  earths,  mixed 
with  a  small  portion  of  lime  or  alumine.  Mr.  Kirwan  con- 
fines the  term  to  the  purer  kind  of  siiex.  Rock  crystal  and 
the  amethyst  are  species  of  quartz. 

R. 

Radicals.  A.  chemical  term  for  the  Elements  of  bodies; 
which  see. 

compound.  When  the  base  of  an  acid  is  composed 

of  two  or  more  substances,  it  is  said  that  the  acid  is  formed 
of  a  compound  radical.  The  sulphuric  acid  is  formed  with 
a  simple  radical;  but  the  vegetable  acids,  which  have  radicals 
composed  of  hydrogen,  and  carbon,  are  said  to  be  acids  with 
compound  radicals. 

Reagents.  Substances  which  are  added  to  mineral  waters  or 
other  liquids  as  tests  to  discover  their  nature  and  composition. 

Realgar,     lied  sulphurretted  oxide  of  arsenic. 

Receivers.     Globular  glass  vessels  adapted  to  retorts  for  the 


358  A  VOCABULARY 

purpose  of  preserving  and  condensing  the  volatile  matte  t 
raised  in  distillation. 

Rectification,  is  nothing  more  than  the  re-distilling  a  liquid  to 
render  it  more  pure,  or  more  concentrated,  by  abstracting  a 
part  of  it  only. 

Reduction.  The  restoration  of  metallic  oxides  to  their  origi- 
nal state  of  metals ;  which  is  usually  effected  by  mean.*  of 
charcoal  and  fluxes. 

Refining.  The  process  of  separating  the  perfect  metals  from 
other  metallic  substances,  by  what  is  called  cupellation. 

Refrigeratory.  A  contrivance  of  any  kind,  which,  by  con- 
taining cold  water,  answers  the  purpose  of  condensing  the  va- 
pour or  gas  that  arises  in  distillation.  A  worm-tub  is  a  re- 
frigeratory. 

Regulus.  In  its  chemical  acceptation,  signifies  a  pure  metallic 
substance,  freed  from  all  extraneous  matters. 

Repulsion.  A  principle  whereby  the  particles  of  bodies  are 
prevented  from  coming  into  actual  contact.  It  is  thought  to 
be  owing  to  caloric,  which  has  been  called  the  repulsive 
power. 

Resins.  Vegetable  juices  concreted  by  evaporation  either  spon- 
taneously or  by  fire.  Their  character  is  solubility  in  alcohol, 
and  not  in  water.  It  seems  that  they  owe  their  solidity  chief- 
ly to  their  union  with  oxygen. 

Retort.     A  vessel  in  the  shape  of  a  pear,  with  its  neck   bent 
downwards,  used  in  distillation;  the  extremity  of  which  neck 
fits  into  that  of  another  bottle  called  a  receiver. 
Rock-crystal.     Crystallized  silex. 

S, 

Saccholates.  Salts  formed  by  the  combination  of  any  base 
with  saccholactic  acid. 

Salifiable  bases.  All  the  metals,  alkalies,  and  earths,  which 
are  capable  of  combining  \,ith  acids,  and  forming  salts,  are 
called  salifiable  bases. 

Saline.     Partaking  of  the  properties  of  a  salt. 

Salts  neutral.  A  class  of  substances  formed  by  the  combina- 
tion to  saturation  of  an  acid  with  an  alkali,  an  earth,  or  oth- 
«r  salifiable  base. 

triple.  Salts  formed  by  the  combination  of  an  acid 

with  two  bases  or  radicals.  The  tartrate  of  soda  and  potass 
(Rochelle  salt)  is  an  instance  of  this  kind  of  combination. 

Saponaceous.  A  term  applied  to  any  substance  which  is  of 
the  nature  or  appearance  of  soap. 


OF  CHEMICAL  TERMS.  339 

Saturation.  The  act  of  impregnating  a  fluid  with  another 
substance,  till  no  more  can  be  received  or  imbibed.  A  fluid 
which  holds  as  much  of  any  substance  as  it  can  dissolve,  is 
said  to  be  saturated  with  that  substance.  A  solid  may  in  the 
same  way  be  saturated  with  a  iluid. 

Sebates.  Salts  formed  by  the  combination  of  any  base  with 
sebacic  acid. 

Semi-Metal.  A  name  formerly  given  to  those  metals  which, 
if  exposed  to  the  fire,  are  neither  malleable,  ductile,  nor  fix- 
ed. It  is  a  term  not  used  by  modern  chemists. 

Siliceous  Earths.  A  term  used  to  describe  a  variety  of  natu- 
ral substances  which  are  composed  chiefly  of  silexj  as 
quartz,  flint,  sand,  &c. 

Simple  Substances.     Synonymous  with  Elements;  which  see. 

Smelting.  The  operation  of  fusing  ores  for  the  purpose  of 
separating  the  metals  they  contain,  from  the  sulphur  and  ar- 
senic with  which  they  are  mineralized,  and  also  from  other 
heterogeneous  matter. 

Solution.  The  perfect  union  of  a  solid  substance  with  a  fluid. 
Salts  dissolved  in  water  are  proper  examples  of  solution. 

Spars.  A  name  formerly  given  to  various  crystallized  stones  ; 
such  as  the  fluor  spar,  the  adamantine  spar,  &c.  These 
natural  substances  are  now  distinguished  by  names  which  de- 
note the  nature  of  each. 

Stalactites.  Certain  concretions  of  calcareous  earth  found  sus- 
pended like  icicles  in  caverns.  They  are  formed  by  the 
oozing  of  water,  through  the  crevices,  charged  with  this 
kind  of  earth. 

Steatites.  A  kind  of  stone  composed  of  silex,  iron,  and  mag- 
nesia. Also  called  French  chalk,  Spanish  chalk,  and  soap- 
rock. 

Sub-Salts.  Salts  with  less  acid  than  is  sufficient  to  neutralize 
their  radicals. 

Suberates.  Salts  formed  by  the  combination  of  any  base  with 
the  suberic  acid. 

Sublimation.  A  process  whereby  certain  volatile  substances 
are  raised  by  heat,  and  again  condensed  by  cold  into  a  solid 
form.  Flowers  of  sulphur  are  made  in  this  way.  The  soot 
of  our  common  fires  is  a  familiar  instance  of  this  process. 

Succinates.  Salts  formed  by  the  combination  of  any  base  with 
the  succinic  acid. 

Sulphates.  Salts  formed  by  the  combination  of  any  base  with 
the  sulphuric  acid. 

Sulphites.  Salts  formed  by  the  combination  of  any  base  witk 
the  sulphurous  acid. 


360  A  VOCABULARl 

Sulphures,  or  Sulphurcfs.     Combinations  of  alkalies,  or  n». 
with  ^alphur. 

Sulphuretted.  A  substance  is  said  to  be  sulphuretted  \vliei 
it  is  combined  with  sulphur.  Thus  we  may  say  Sulphuret- 
ted hydrogen,  &c. 

Super  Salts.  Salts  with  an  excess  of  acid,  as  the  superior- 
trate  of  potass. 

Synthesis.  When  a  body  is  examined  by  dividing  it  into  its 
component  parts,  it  is  called  analysis;  but  when  we  at- 
tempt to  prove  the  nature  of  a  substance  by  the  union  of  its 
principles,  the  operation  is  called  synthesis. 

T. 

Tartrates.  Salts  formed  by  the  combination  of  any  bast- 
with  the  acid  of  tartar. 

Temperature.  The  absolute  quantity  of  free  caloric  which  is 
attached  to  any  body  occasions  the  ^degree  of  temperature- 
of  that  body. 

Test.  That  part  of  a  cupel  which  is  impregnated  with  litharge 
in  the  operation  of  refining  lead.  It  is  also  the  name  of 
whatever  is  employed  in  chemical  experiments  to  detect  the 
several  ingredients  of  any  composition. 

Test-Papers.  Papers  impregnated  with  certain  chemical  re- 
agents ;  such  as  litmus,  turmeric,  radish,  &c.  They  are 
used  to  dip  into  fluids  to  ascertain  by  a  change  of  colours  the 
presence  of  acids  and  alkalies. 

Thermometer.  An  instrument  to  show  the  relative  heat  of  bo- 
dies. Fahrenheit's  thermometer  is  that  chiefly  used  in  Eng- 
land. Other  thermometers  are  used  in  different  parts  of  Eu- 
rope. 

Tinrtfires.     Solutions  of  substances  in  spirituous  menstrua. 

Trituration.  A  chemical  operation  whereby  substances  are 
united  by  friction.  Amalgams  are  made  by  this  method. 

Tubulated.  Retorts  which  have  a  hole  at  the  top  for  inserting 
the  materials  to  be  operated  upon  without  taking  them  out  of 
the  sand  heat,  are  called  tubulated  retorts. 

Tungstates.  Salts  formed  by  the  combination  of  any  base  with 
tungstic  acid. 

V, 

Vacuum.  A  space  unoccupied  by  matter.  The  term  is  gen 
erally  applied  to  the  exhaustion  of  atmospheric  air  by  chem- 
ical or  philosophical  means. 


OF    CHEMICAL    TERMS.  30! 

Vapour.  This  term  is  used  by  chemists  to  Denote  such  exhala- 
tions only  as  can  be  condensed  and  rendered  liquid  again  at 
the  ordinary  atmospheric  temperature,  in  opposition  to  those 
which  are  permanently  elastic. 

Vital  Air.  Oxygen  gas.  The  empyreal  or  fire-air  of  Scheele, 
and  the  dephlogisticated  air  of  Priestly. 

Vitrification.  When  certain  mixtures  of  solid  substances,  such 
as  silex  and  an  alkali,  are  exposed  to  an  intense  heat,  so  as 
to  be  fused,  and  become  glass,  they  are  then  said  to  be  vitri- 
fied, or  to  have  undergone  vitrification. 

Vitriols.  A  class  of  substances,  either  earthy  or  metallic,  which 
are  comUned  with  the  vitriolic  acid.  Thus  there  is  vitriol 
of  lime,  vitriol  of  iron,  vitriol  of  copper,  &c.  These  salts 
are  now  called  Sulphates,  because  the  acid  which  forms  them 
is  called  sulphuric  acid. 

Vitriolated  Tartar.     The  old  name  for  sulphate  of  potass. 

Volatile  Alkali.     Another  name  for  ammonia. 

Volatile  Salts.  The  commercial  name  for  carbonate  of  ammo, 
nia. 

Volatility.  A  property  of  some  bodies  which  disposes  them 
to  assume  the  gaseous  state.  This  property  seems  to  be  ow- 
ing to  their  affinity  for  caloric. 

Volume.  A  term  made  use  of  by  modern  chemists  to  express 
the  space  occupied  by  gaseous  or  other  bodies. 

u. 

Union  chemical.  When  a  mere  mixture  of  two  or  more  sub- 
stances is  made,  they  are  said  to  be  mechanically  united ;  but 
when  each  or  either  substance  forms  a  component  part  o! 
the  product,  the  substances  have  formed  a  chemical  union. 

W. 

JVater.  The  most  common  of -all  fluids,  composed  of  85  parts 
of  oxygen  and  15  of  hydrogen. 

mineral.     Waters  which  are  impregnated  with  mineral 

and  other  substances  are  known  by  this  appellation.  These 
minerals  are  generally  held  in  solution  by  carbonic,  sulphur- 
ic, or  muriatic  acid. 

Way,  dry.  A  term  used  by  chemical  writers  when  treating  of 
analysis  or  decomposition.  By  decomposing  in  the  dry  way, 
is  meant,  by  the  agency  of  fire. 

Way  humid.    A  term  used  in  the  same  manner  as  the  forego 

32 


^2        A  VOCABULARY  OF  CHEMICAL'  TERMS. 

ing,  but  expressive  of  decomposition  in  a  fluid  state,  or  by 

means  of  water,  and  chemical  re-agents,  or  tests. 
Welding  Heat.     That  degree  of  heat  in  which  two  pieces  of 

iron  or  of  platina  may  be  united  by  hammering. 
Wolfram.     An  ore  of  tungsten  containing  also  manganese  and 

iron. 
Worm-Tub.     A  chemical  vessel  with  a  pewter  worm  fixed  in 

the  inside,  and  in  the  intermediate  space  filled  with  water. 

Its  use  is  to  cool  liquors  during  distillation. 
Woulfe's  apparatus.     A  contrivance  for  distilling  the  mineral 

acids  and  other  gaseous  substances  with  little  loss  ;  being  a 

train  of  receivers  with  safety-pipes,  and  connected  together 

by  tubes. 

Z. 

Zafre.  An  oxide  of  cobalt,  mixed  with  a  portion  of  siliceous 
matter.  It  is  imported  in  this  state  from  Saxony. 

Zero.  The  point  from  which  the  scale  of  a  thermometer  is 
graduated.  Thus  Celsius's  and  Reaumur's  thermometers 
have  their  zero  at  the  freezing  point,  while  the  thermometer 
of  Fahrenheit  has  its  zero  at  that  point  at  which  it  stands 
when  immersed  in  a  mixture  of  snow  and  common  salt. 


LIST  OF  EXPERIMENTS. 

IN  making  up  the  following  list  of  experiments  I  have 
careful  in  general  to  select  such  as  can  be  made  with  safety  to 
the  young  student ;  where  this  is  not  the  case  the  caution  is 
mentioned.  Most  of  them  require  but  very  simple  apparatus. 
Where  any  experiment  illustrates  the  text,  a  reference  is  made 
to  the  page.  Some  of  them  are  original,  others  are  borrowed, 
I  have  not  however  deemed  it  necessary  to  cite  authors. 

1.  To  show  that  heat  is  not  absorbed,  but  reflected  by  pol- 
ished metallic  surfaces,  hold  a  common  new  tin-pan  before  the 
fire.     The  pan  will  remain  cold.     See  p.  29- 

2.  To  show  the  power  of  a  black  surface  to  absorb  caloric, 
smoke,  or  paint  black  a  spot  of  the  size  of  a  dollar  on  the  bot- 
tom of  the  tin-pan;  and,  hold  it  towards  the  fire.     On  touching 
this  spot,  it  will  be  found  hot,  while  the  parts  around  it  remain 
cold.     See  p.  31. 

3.  To  make  the  upper  part  of  a  vessel  of  water  boil,  while 
there  is  a  cake  of  ice  at  the  bottom.     Into  a  glass  tube  put  wa- 
ter enough  to  occupy  two  inches.     Freeze  this,  so  as  not  to 
burst  the  tube,   with  a  freezing  mixture,  or  by  exposure  to  cold 
in    winter.     Then  fill  the  tube  nearly  full  of  water,  and  wind 
a  flannel  clotl^everal  times  around  the  part  containing  the  ice, 
so  that  the  heat  of  the  hand  will  not  melt  it.     Then  hold  the 
tube  in  an  oblique  direction  over  a  lamp,  so  as  to  heat  the  wa- 
ter an  inch  or  two  above  the  ice.     The.  water  will  soon   begin 
to  boil,  and  by  raising  the  tube  a  little  at  a  time,  it  will  boil  al- 
most to  the  surface  of  the  ice,   without  melting  it.     See  p.  39. 

4.  To  show  that  some  of  the  metals  conduct  caloric  better 
than  others,  procure  wires  of  the  same  size  and  length,  of  gold, 
silver,  copper,  iron,  zinc,  tin,  &c.     The  wires  maybe  12  or 
14  inches  long.     Coat  one  end  of  each  with  bees- wax,  and  put 
the  other  ends  into  a  vessel  of  hot  water.     The  wax  will  melt 
first  on  the  metal  which  is  the  best  conductor,  and  the  compar- 
ative conducting  powers  are  calculated  by  the  difference  of  tinve 
between  the  melting  of  the  wax  on  each.     See  p.  35. 

5.  The  conducting  powers  of  different   substances  in  regard 
to  caloric,  may  be  much  more  sensibly  elucidated,  by  touching  in 
cold  weather,  a  metal  with  one  hand,  and  a  piece  of  cork,  wood, 
or  cloth  with  the  other.     Here  the   sensation  of  cold,  to  the 
hand  which  touches  the  metal,  is  owing  to  the  power  which  all 


364  EXPERIMENTS, 

metals  have  of  conducting  off  heat,  more  rapidly  thauaiiy  oth- 
er class  of  substances.     See  p.  37. 

6.  To  show  that  evaporation  carries  off  caloric,  moisten  tbr 
bulb  of  a  thermometer  tube  with  ether,  by  means  of  a  hair  pen- 
cil. The  mercury  immediately  begins  to  fail,  and  if  the  pro- 
cess be  continued,  may  be  brought  down  to  the  freezing  point, 
even  in  warm  weather.  Whenever  a  fluid  substance  is  con- 
verted  into  vapour,  it  absorbs  a  quantity  of  caloric.  In  the 
present  case,  the  ether  takes  from  the  bulb  of  the  thermometer, 
the  caloric  necessary  to  give  it  the  elastic  form.  Therefore, 
every  new  application  of  the  ether  carries  off  successive  por- 
tions of  heat,  and  the  mercury  continues  to  sink,  until  the  bulb 
becomes  so  cold,  as  to  absorb  caloric  from  the  surrounding 
air,  faster  than  it  is  carried  off  by  the  evaporation.  This  is 
the  reason  why  the  mercury  cannot  be  depressed  below  a  cer- 
tain point  by  evaporation.  The  ether,  although  it  assumes  the 
elastic  form,  does  not  receive  the  caloric  necessary  for  this  pur- 
pose from  the  thermometer,  but  from  the  surrounding  air. 
See  p.  53. 

7-  To  demonstrate  that  fluids  boil  at  comparatively  small  de- 
grees of  heat,  when  the  pressure  of  the  atmosphere  is  taken  off, 
about  half  fill  with  water  a  small  retort,  or  Florence  flask  (com- 
mon oil  flask,)  and  let  it  boil  over  a  lamp.  When  the  upper 
part  is  filled  with  steam,  take  it  from  the  lamp,  and  instantly 
cork  it  air  tight.  If  now  it  is  put  into  cold  water,  it  begins  to 
boil  violently.  If  taken  out  of  the  water,  it  stops  boiling,  and 
this  may  be  done  many  times.  This  curious  method  of  mak- 
ing water  boil  by  the  application  of  cold,  is  easily  accounted 
for.  When  the  flask  is  put  into  cold  water,  the  steam  with 
which  it  was  filled,  is  condensed  and  returns  again  to  water 
This  leaves  a  vacuum*  in  which  water  is  converted  into  steam,, 
or  boils,  at  a  much  lower  temperature  than  in  the  open  air. 
See  p.  55. 

8.  If  the  above  experiment  is  made  by  means  of  a  small  re- 
tort, a  very  curious  circumstance  may  be  observed  :  When  the 
water    is  cold,  and  consequently   nearly  a  perfect  vacuum   is 
formed,  if  the  retort  is  shaken,  there  is  produced  a  sharp  rattling 
noise,  as  though  it  contained  shot,  instead  of  water,   so  that  one 
would  suppose  by  the  noise  that  the  retort  would  be  broken  in- 
to a  thousand  parts  at  every  motion.     This  is   owing   to  the 
weight  with  which  the  water  falls  upon  the  glass,  when  there  is 
no  air  to  impede  its  motion. 

9.  Into  a  thin  glass  vessel,  pour  an  ounce  or  two  of  water, 
and  then  pour  in  two  drams  of  sulphuric  acid;  the  glass  will 
instantly  become  too  hot  to  be  held  in  the  hand.     This  expert- 


EXPERIMENTS.  365 

ment  elucidates  the  doctrine  of  latent  heat.  On  mixing  these 
two  fluids,  a  chemical  combination  takes  place  between  their 
particles,  in  consequence  of  which  caloric  is  extricated,  at  the 
same  time  their  bulk  is  diminished.  This  also  illustrates  Dr. 
Black's  law.  that  when  substances  pass  from  a  rarer  to  a  denser 
state,  caloric  is  given  out.  If  one  measure  of  sulphuric  acid, 
and  one  of  water,  be  mixed  together,  the  mixture  will  not  again 
till  the  measure  twice.  See  p.  69. 

10.  To  procure  nitrogen,  take  a  bell  glass,  or  large  tumbler, 
and  invert  it  over  a  short  taper,  set  in  a  shallow  dish   of  water. 
The  taper  burns  until  it  absorbs  all  the  oxygen  contained  in  the 
air  under  the  bell  glass.     What  remains   is   nitrogen.     If  now 
a  lighted  taper  be  put  under  the  bell  glass,  it  will  be  instantly 
extinguished,  showing  the  absolute  necessity  of  oxygen  for  the 
support  of  combustion.     See  p.  85,  89. 

11.  The  formation  of  water  by  the   burning  of  hydrogen 
may  be  shown  thus :  Take  a  Florence  lias k  and   pour  into  it 
half  a  pint  of  water,  then  put  in  about  an  ounce  of  granulated 
zinc,  or  the  same  quantity  of  iron  filings,  and  then  pour  in  halt 
an  ounce  by  measure  of  sulphuric  acid.      Have  ready  a  cork, 
pierced  with  a  burning  iron,   and  the  stem  of  a   tobacco   pipe 
passed  through  the.  aperture.     After  putting  in  the  acid,   put 
the  cork  in  its  place,  and  fix  the  flask  upright  by  setting  it   in   a 
bowl,  surrounded  by  a  cloth,  to  make  it  stand  up  and   prevent 
its  breaking.     As  the  hydrogen  is  formed,  it  issues  through  the 
stem  of  the  tobacco  pipe,  at  the  end  of  which  it  is  to  be  fixed. 
If  now  a  glass  tube  two  or  three  feet  long  and  an  inch  or  two 
wide  be  passed  on  to  the  stem  so  as  to  include  the  flame  within 
its  bore,  the  tube,  in  a  few  moments  will  be  covered  on  tae  in- 
side with  moisture.     See  p.  106. 

If  the  orifice  of  the  tube  is  quite  small  at  the  end  where  the 
gas  is  fired,  the  above  experiment  serves  to  protiuce  the  musical 
tones.  See  p.  108. 

12.  An  exhibition  of  gas  light  may  be  made  as  follows  :  In- 
to the  bowl  of  a  common  tobacco  pipe  put  a  piece  of  mineral,  or 
what  is  called  sea-coal,  and  cover  the  coal  closely  with  clay. 
When  the  clay  is  dry,  place  the  bowl  in  the  fire   and  heat  it 
slowly.     In  a  few  minutes  the  gas,  called  carburetted  hydrogen 
will  issue  from  the  end  of  the  pipe  stem  ;  set  fire  to  it  with  a 
candle,  and  it  will  burn  with  a  beautiful  bright  flame.     This  is 
gas  with  which  the  streets,  factories  &c.  are  lighted  in  many  01 
the  European  cities. 

In  the  absence  of  mineral  coal,  a  walnut,  small  piece  of  pine 
knot,  or  butternut  meat  &c.  may  take  the  place  of  the  coal 
See  p.  114. 

32* 


EXPERIMENTS. 


13.  The  following  gives  an  example  of  the  manner  in  which 
sulphuric  acid  is  formed. 

Mix  with  a  small  quantity  of  the  flowers  of  sulphur,  about 
one  fifth  part  of  finely  pulverized  nitre.  Make  a  stand  by  hol- 
lowing with  a  hammer  a  large  button,  and  attaching  wire  to  the 
eye,  for  feet,  so  that  the  button  will  be  two  inches  high; — or  by 
any  other  means,  place  the  sulphur  and  nitre  about  this  heighth 
in  a  shallow  dish,  containing  an  inch  or  two  of  water.  Set  fire 
to  the  mixture  with  a  hot  iron,  and  immediately  invert  over  it 
a  bell  glass,  or  large  tumbler.  The  sulphur,  as  it  burns,  ab- 
sorbs oxygen  from  the  air  contained  under  the  bell  glass,  in  a 
proportion  which  would  constitute  sulphuroi/s  acid.  At  the 
same  time  the  heat  which  this  process  occasions,  compels  the 
nitre  to  give  out  another  proportion  of  oxygen,  which  is  absor- 
bed by  the  sulphurous  acid,  and  this  additional  quantity  of  ox- 
ygen, constitutes  sulphuric  acid.  See  p.  121. 

14.  Take  three  parts  of  nitre,  two  of  potash  and  one  of  sul- 
phur, and  mix  them  intimately,  by  rubbing  in  a  mortar.     This 
compound  is  called  fulminating  powder.     On  placing  a   little 
of  it  on  a  shovel  over  a  hot  fire,  it  explodes   with  great  vio- 
lence, and  with  a  peculiarly  stunning  report. 

15.  The  combustion  of  phosphuretted  hydrogen  in  oxygen 
gas,  affords  one  of  the  most  striking,   and   beautiful,   among 
chemical  experiments.     It  is  done  as   follows:     Take  some 
phosphuret  of  lime,  wrap  it  in  a  paper  and  push  it  under  a  ves- 
sel, as  a  wide  mouthed  vial,  filled  with   water,  and  inverted  on 
the  shelf  of  theVater  bath.     As  soon  as  the  water  penetrates 
through  the  paper  so  as  to  wet  the  phosphuret  of  lime,  bubbles 
of  phosphuretted  hydrogen,  begin  to  rise  up  through  the  water. 
While  this  is  going  on,  fill  a  strong  glass  vessel,  as  a  tumbler, 
or  a  piece  of  thick  glass  tube  stopped  at  one  end,  with  oxygen 
gas.     Invert  this  also  on  the  shelf  of  the  water  bath.     When 
the  phosphuretted  hydrogen  is  collected,  take  the  vessel  con- 
taining it  in  one  hand,  and  that  containing  the   oxygen  in  the 
other  ;  bring  the  mouth  of  the  former,  by  sinking  it  deeper  in  the 
water,  under  the  edge  of  the  latter  vessel,  then  by  carefully  de- 
pressing the  bottom  of  the  vessel  containing  the  phosphoretted 
hydrogen,  let  up  a  bubble  at  a  Vime  into  the  oxygen  gas.     If 
this  experiment  is  made  in  a  darkened  room,  the  Bashes  of  light 
appear  astonishingly  vivid  and  beautifuh     See  p.  126. 

16.  Take  six  or  eight  grains  of  oxy-muriat  e  of  potash,  put  it 
into  a  mortar  and  drop  in  with  it  about  a  grain  of  solid  phospho- 
rus, cut  into  two  or  three  parts;  then  rub  them  together  with 
the  pestle.     Very  violent  detonations  are  produced  by  these 
small  quantities.     It  is  best,  therefore,  not  to  use  more  than  is 


EXPERIMENT?,  367 

jiere  mentioned  at  a  time.     The  hand  holding  the  pestle  ought 
always  to  be  protected  with  a  glove  or  handkerchief. 

17.  To  make  liquid  phosphorus,  take  an  ounce  vial  and  half 
fill  it  with  olive  oil,  and  put  into  the  oil  a  piece  of  phosphorus  of 
the  size  of  a  pea  ;  gradually  heat  the  bottom  of  the  vial,  until 
the  phosphorus  is  melted,  taking  care  to  keep  the  thumb  on  the 
mouth  ;  then  cork  it  air  tight.     If  this  vial  is  first  shaken,  and 
then  the  cork  be  taken  out,  it  becomes  luminous,  first  near  the 
mouth,  and  gradually  down  to  the  oil,  at  the  bottom.     The  light 
which  a  bottle  prepared  in  this  way  gives,  particularly  if  warm- 
ed, by  holding  it  in  the  hand,  is  sufficient  to  tell  the   hour  of 
night  by  a  watch.     This  luminous  appearance,  when  the  cork 
is  removed,  is  owing  to  the  union  of  the  oxygen  of  the  atmos- 
phere with  the  phosphorus.     It  is  a  slow  combustion,  attended 
with  light,  and  most  probably  with  some  heat. 

18.  If  drawings  be  made  on  silk  with  a  solution  of  nitrate  of 
silver,  and  the  silk  first  moistened,  is  exposed  to  a  stream  of  hy- 
drogen gas,  or  in  any  other  way  exposed  to  the  action  of  this  gas, 
the  metal  is  instantly  revived,  and  the  silk  is  covered  with  fig- 
ures of  silver.     See  p.  147. 

iy.  If  a  few  drops  of  a  solution  of  nitrate  of  silver  in  water, 
be  placed  on  a  bright  surface  of  copper,  the  silver  is  revived, 
and  gives  the  copper  a  brilliant  white  coat  of  that  metal.  This 
is- explained  on  the  principle  of  affinity.  The  copper  has  a 
stronger  attraction  for  the  acid  which  composes  a  part  of  the 
nitrate  of  silver,  than  the  silver  itself  has.  Therefore  it  attracts 
the  acid  from  the  silver,  in  consequence  of  which  this  is  receiv- 
ed, and  at  the  same  time  precipitated  on  the  copper.  See  p. 
147. 

20.  Take  a  little  of  the.white  arsenic  of  the  shops,  and   mix 
it   with  some  fineU    ground  charcoal;  put  the  mixture  into  a 
small  glass  tube  closed  at  one  end,  and  expose  the  part  where 
the  mixture  is  to  a  moderate  degree  of  heat  gradually  raised  • 
the  arsenic  will  be  received,  and  will  attach  itself  to  the  upper 
part  of  the  tube,  giving  it  a  brilliant  metallic  coat  like  quick 
silver.     The  arsenic  may  be  preserved  in  this  state  by  stopping 
up  the  tube.     See  p.  149- 

21.  Dissolve  a  teaspoonfull  of  sugar  of  lead  in  a  quart  of 
rain  water.     Put  this  into  a  decanter,  or  white  glass  bottle,  and 
suspend  in  it  by  means  of  a  string  a  piece  of  zinc.     The  zinc 
decomposes  the  acetate  of  lead  by  depriving  it  of  its  oxygen  ; 
the  consequence  is  that  the  lead  is  precipitated  in  the  metallic 
state  on,  and  around  the  zinc,  and  forms  a  brilliant  tree  of  me- 
tal 

22.  Pour  a  solution  of  nitrate  of  silver  into  a  glass  vessel 


368  EXPERIMENTS. 

and  immerse  a  few  slips  of  copper  in  it.  In  a  short  time  a 
portion  of  copper  will  be  dissolved,  and  all  the  silver  precipi- 
tated in  a  metallic  forai.  If  the  solution  which  now  contains 
copper  be  decanted  into  another  glass,  and  pieces  of  iron  ad- 
ded to  it,  this  metal  will  then  be  dissolved,  and  the  copper  pre- 
cipitated, yielding  a  striking  instance  of  peculiar  affinities. 
See  p.  170. 

23.  Ivory  may  be  coated  with  silver  by  the  following  pro- 
cess.    Make  a  strong  solution  of  nitrate  of  silver  in  pure  wa- 
ter; into  this  immerse  a  piece  of  ivory  until   it  turns  yellow  ; 
then  take  it  out  and  immediately  plunge  it  into  a  vessel   of  dis- 
tilled water  exposed  to  the  direct  rays  of  the  sun  until  it  turns 
black.     On  rubbing  it  gently -it  will   appear  covered   with  a 
brilliant  coat  of  silver,  resembling  a  bar  of  that   metal.     This 
curious  effect  is  owing  to  the  solar  light  which  decomposes  the 
nitrate  silver  by  taking  the  oxygen  from  it,   which  flies   off  in 
the  form  of  oxygen  gas. 

24.  Through  a  vessel  of  lime   water,  recently   made,   pass 
bubbles  of  carbonic  acid  gas  by  means  of  a  bladder  and  tube, 
the  lime  water  instantly  becomes  white  and  turbid,  and  finally 
deposits  a  quantity  of  carbonate  of  lime  in  the  form   of  pow- 
dered chalk.     If  now  the  water  be  evaporated  a  white  powder 
remains  which  effervesces  with  acids.     If  this   powder   is  put 
into  a  retort,  and  sulphuric  acid  diluted  with   water  is  poured 
upon  it,  the  beak  of  the  retort  being  under  a  vessel  tilled  with 
water,  the  carbonic  acid  is  again  obtained,  and  the  salt  remain- 
ing in  the  retort  will  be  sulphate  of  lime,  or  gypsum. 

25.  Mix  one  part  of  nitric  acid  with  5  or  6  parts  of  water  in 
a  vial ;  into  this  put  some  copper  filings,  and  in  a  few  moments 
pour  off  the  liquid  ;  it  will  be  colourless.     If  now  there  be  ad- 
ded some  liquid  ammonia,  another  colourless  fluid,  the  mixture 
becomes  of  an  intense  and  beautiful  blue.     Hence  ammonia  is 
a  most  delicate  test  for  the  presence  of  copper,  with  which  it 
strikes  a  deep  blue  colour.     See  p.  180. 

26.  Put  into  a  vial  of  pure  water  a  few  drops  of  tire  tincture 
of  nut  galls,  made  by  steeping  the  galls  hi  water;  into  another 
vial  of  pure  water  put  a  grain  or  two  of  the  sulphate  of  iron.    If 
these  colourless  fluids  are  mixed,  they  instantly  become  black, 
Tincture  of  galls  is  a  most  delicate  test  for  the  presence  of  iron, 
with  which  it  strikes  a  black.     These  two  substances  form  the 
basis  of  ink.     See  p.  180. 

27.  Take  two  small  glass  jars,  or  tumblers,  and  fill  one  with 
carbonic  acid  gas  7  and  the  other  with  oxygen  gas.     Have  them 
set  upright  with  a  cover  on  each.     If  a  lighted  taper  be  plunged 
into  the  vessel  containing  the  carbonic  acid?  it  is  extinguished 


EXPERIMENTS. 

instantly;  but  if  it  is  immediately  plunged  into  the  other  jar 
containing  the  oxygen,  it  is  as  instantly  lighted  with  a  sort  of 
explosion.  See  p.  2l9« 

28.  Put  eight  or  ten  grains  of  oozy-muriate  of  potash  into  a 
teacup,  and  then  pour  in  two  or  three  drams  of  alcohol — If  now 
about  two  drams  of  sulphuric  acid  is  added,  the  mixture  begins 
to  dart  forth  little  balls  of  blue  fire,  and  in  a  minute  or  two.  the 
whole  bursts  into  flame.     The  alcohol  is  inflamed  by  the  clo- 
rine  which  is  set  free  from  the  salt,  in  consequence  of  the  com- 
bination which  takes  place  between  the  potash  and  sulphuric 
acid.     See  p.  233. 

29.  Into  a  glass  tube  half  an  inch  or  an  inch  wide,  two  or 
three  inches  long,  with  a  bulb  at  the  end,  put  a  grain  or  two 
of  iodine.      Warm  the  tube,  (but  not  at  that  part  where  the 
iodine  is,)  and  immediately  cork  it  tight;  the  tube  remains  co- 
lourless, there  being  only  a  few  little  specks  here  and  there.    If 
at  any  time  the  tube  be  warmed  at  that  part  where  the;  iodine  is, 
it  is  instantly  filled  with  a  gas  of  a  most  beautiful  violet  colour. 
If  care  is  taken  to  keep  the  tube  well  closed,  so  that  the  iodine 
does  not  escape,  when  it  takes  the  form   of  gas,  this  effect  will 
always  be   produced   whenever  the  tube  is  warmed.     A  tube 
with  two  bulbs,  like  what  is  called  a  pulse  glass ,  containing  the 
iodine  hermetically  sealed,  would  be  better.    ,  Such  a  little  ap- 
paratus would  be  quite  a  curiosity  to  those   who  know  nothing 
of  the  nature  of  iodine.  See  p.  235. 

30.  Write  on  paper  with  a  solution  of  the  nitrat  of  silver, 
taking  care  not  to  have  it  so  strong  as  to  destroy  the  paper. 
So  long  as  it  is  kept  in  the  dark,  or  if  the  paper  be  closely  fol- 
ded, the  writing  remains  invisible;  but  on  exposure  to  the  rays 
of  the  sun  the  characters  turn  yellow,  and  finally  black,  so  that 
they  are  perfectly  legible. 

Mr.  Accum  says,  that  this  change  of  colour  is  owing  to  the 
partial  reduction  of  the  oxide  of  silver  from  the  light  expelling 
a  portion  of  its  oxyeen  ;  the  oxide  therefore  approaches  to  the 
metallic  state;  for  when  the  blackness  is  examined  with  a  deep, 
or  powerful  magnifier,  the  particles  of  metal  may  be  distinctly 
seen . 

3t.  Write  on  paper  with  a  dilute  solution  of  common  sugar 
of  lead  ;  the  writing  will  remain  invisible.  But  on  moistening 
the  lines  with  a  pencil,  or  leather  dipped  in  water  impregnated 
with  sulphuretted  hydrogen,  the  metal  is  rev:ved,  and  the  let- 
ters appear  in  metallic  brilliancy. 

The  author  above  cited,  says,  that  in  this  instance,  the  hy- 
drogen of  the  sulphuretted  hydrogen  gas,  abstracts  the  oxygen 
from  the  oxide  of  lead,  and  causes  it  to  re-approach  to  the  me- 


3/0  EXPERIMENTS. 

tallic  state  ;  at  the  same  time,  the  sulphur  of  the  sulphuretted 
hydrogen  gas  combines  with  the  metal  thus  regenerated,  and 
converts  it  into  a  sulphuret,  which  exhibits  the  metallic  colour. 

32.  Write  on  paper  with  a  solution  of  the  sulphate  of  cop- 
per.    If  this  is  strong,  the  writing  will  be  of  a  faint  green  col- 
our ;  if  weak  the  characters  are  invisible.     On  holding  the  pa- 
per over  a  vessel  containing  some   liquid  ammonia,  or  if  it  be 
exposed  to  the  action  of  this  gas  in  any  other  way,  the  writing 
assumes  a  beautiful  blue  colour.     On  exposing  the  paper  to  the 
sun  the  colour  disappears,  because  the  ammonia  evaporates. 

33.  Put  a  small  piece  of  phosphorus  into  a  crucible,  cover 
it  closely  with  common  chalk,  so  as  to  fill  the  crucible.     Let 
another  crucible  be  inverted  upon  it,  and  both  subjected  to  the 
fire.     When  the  whole  has  become  perfectly  red-hot,  remove 
them  from  the  fire,  and   when  cold,  the  carbonic  acid  of  the 
chalk  will  have  been  decomposed,  and  the  Black  Charcoal,  the 
basis  of  the  acid,  may  be  easily  perceived  amongst  the  mate- 
rials. 

34.  Into  a  large  glass  jar,  inverted   upon  a  flat  brick  tile, 
and  containing  near  its  top  a  branch  of  fresh  rosemary,   or  any 
other  such  shrub,  moistened  with  water,  introduce  a  flat  thick 
piece  of  heated  iron,  on  which  place  some  gimi  benzoin  in  gross 
powder.     The  benzoic  acid,  in  consequence  of  the  heat,  will 
be  separated,  and  ascend  in  white  fumes,  which  will  at  length 
condense,  and  form  a  most  beautiful  appearance  upon  the  leaves 
of  the  vegetable.     This  will  serve  as  an  example  of  Sublima- 
tion. 

35.  Mix  a  little  acetate  of  lead  with  an  equal  portion  of 
sulphate  of  zinc,  both  in  fine  powder  ;  stir  them  together  with 
a  piece  of  glass  or  wood,  and  no  chemical  change  will  be  per- 
.eeptible  :  but  if  they  be  rubbed  together  in  a  mortar,  the  two 
solids  will  operate  on  each  other ;  an   intimate  union  will  take 
place,  arid  a  fluid  will  be  produced.     If  alum  or  Glauber  salt 
be  used  instead  of  sulphate  of  zinc,  the  experiment  will   be 
equally  successful. 

3&     [f  the  leaves  of  a  phnt,  fresh  gathered,  be  placed  in  the 
sun,  very  pure  oxygen  gas  may  be  collected. 

37.  Put  a  little  fresh  calcined  magnesia  in  a  tea-cup  upon 
the  hearth,  and  suddenly  pour  over  it  as  much  concentrated  sul- 
phuric acid  as  will  cover  the  magnesia.     In  an  instant  sparks 
will  be  thrown  out,  and  the  mixture  will  be  completely  ignited. 

38.  If  a  few  pounds  of  a  mixture  of  iron  filings  and  sulphur 
be  made  in  paste  with   water,  and    buried  in  the  ground  for  a 
few  hours,  the  water  will  be  decomposed  with  so  much  rapidi- 
ty, that  combustion  and  flame  will  be  the  consequence. 


EXPERIMENTS.  SfJ 

39.  For  want  of  a  proper  g!ass  vessel,  a  table  spoonful   oi 
ether  maybe  put  into  a  moistened  bladder,  and  the  neck  of  the 
bladder  closely  tied.     If  hot  water  be  then  poured  upon  it,  the 
ether  will  expand,  and  the  bladder  become  inflated. 

40.  Procure  a  phial  with  a  glass  stopper  accurately   ground 
[nto  it ;  introduce  a  few  copper  filings,  then  entirely  fill  it  with 
liquid  ammonia,  and  stop  the  phial  so  as  to   exclude  all  atmos- 
pheric air.     If  left  in  this  state,  no  solution  of  the  copper  will 
be  effected.     But  if  the  bottle  be  afterwards  left  open  for  some 
time,  and  then  stopped,  the  metal  will  dissolve,  and  the   solu- 
tion will  be  colourless.     Let  the  stopper  be  now  taken  out,  and 
the  fluid  will  become  blue,  beginning  at  the  surface,  and  spread- 
ing gradually  through  the  whole.     If  this  blue  solution  has  not 
been  too  long  exposed  to  the  air,  and  fresh  copper  filings  be  put 
in,  again  stopping  the  bottle,  the  fluid  will  once  more  be   depri- 
ved of  its  colour,  which  it  will  recover  only  by  the  re-admis- 
sion of  air.     These  effects  may  thus  be  repeatedly  produced. 

41.  If  a  spoonful  of  good  alcohol  and   a  little  boracic  acid 
be  stirred  together  in  a  tea-cup,  and  than  set  on  fire,  they  will 
produce  a  very  beautiful  green  flame. 

42.  Alloy  a  piece  of  silver  with  a  portion  of  lead,  place  the 
alloy  upon  a  piece  of  charcoal,  attach  a  blow-pipe  to  a  gasome- 
ter charged  with  oxygen  gas,  light  the  charcoal  first  with  a  bit 
of  paper,  and  keep  up  the  heat  by  pressing  upon  the  machine. 
When  the  metals  get  into  complete  fusion,  the  lead  will  begin  to 
burn,  and  very  soon  will  be  all  dissipated   in  a  white  smoke, 
leaving  the  silver  in  a  state  of  .purity.     This  experiment  is  de- 
signed to  show  the  fixity  of  the  noble  metals. . 

43.  Burn  a  piece  of  iron  wire  in  a  deflagrating  jar  of  oxygen 
gas,  and  suffer  it  to  burn  till  it  goes  out  of  itself.     If  a  lighted 
wax  taper  be  now  let  down  into  the  gas,  this  will  burn  in  it  for 
some  time,  and  then  become  extinguished.     If  ignited  sulphur 
be  now  introduced,  this  will  also  burn  for  a  limited  time.    Last- 
ly, introduce  a  morsel  of  phosphorus,  and  combustion  will  also 
follow  in  like  manner.     These  experiments  show  the  relative 
combustibility  of  different  substances. 

44.  Drop  a  piece  of  phosphorus  about  the  size  of  a  pea  into 
a  tumbler  of  hot  water,  aad  from  a  bladder,  furnished  with  a  stop 
cock,  force  a  stream  of  oxygen  gas  directly  upon  it.     This  will 
afford  the  most  brilliant  combustion  under  water  that  can  be 
imagined. 

45.  Take  a«i  amalgam  of  lead  and  mercury,  and  another 
amalgam  of  bismuth,  let  these  two  solid  amalgams  be  mixed  by 
triture,  and  they  will  instantly  become  fluid. 

46.  Into  distilled  water  drop  a  little  spirituous  solution  of 


372  EXPERIMENTS. 

soap,  no  chemical  effect  will  be  perceived ;  but  if  some  ot 
the  same  solution  be  added  to  hard-water,  a  milkiness  will  im- 
mediately be  produced,  moie  or  less,  according  to  the  degree  oi 
its  impurity.  This  is  a  good  method  of  ascertaining  the  purity 
of  spring  water. 

47.  To  silver  copper,  or  brass.     Clean  the  article  intended 
to  be  silvered,  by  means  of  dilute  nitric  acid,  or  by  scouring  it 
with  a  mixture  of  common  salt  and  alum.     When  it  is  perfectly 
bright,  moisten  a  little  of  the  powder,    known  in  commerce  by 
the  name  of  silvering"  powder ,  with  water,  and  rub  it  for  some 
time  on  the  perfectly  clean  surface  of  copper,  or  brass,  which 
will  become  covered  with  a  coat  of  metallic  silver.     It  may  af- 
terwards be  polished  with  soft  leather. 

The  silvering  powder  is  prepared  in  the  following  manner : 
Dissolve  some  silver  in  nitric  acid,  and  put  pieces  of  copper  into 
the  solution  ;  this  will  throw  down  the  silver  in  a  state  of  metal- 
lic powder.  Take  fifteen  or  twenty  grains  of  this  powder,  and 
mix  with  it  two  drachms  of  acidulous  tartarite  of  potash,  the 
same  quantity  of  common  salt,  and  half  a  drachm  of  alum. 
Another  method  :  Precipitate  silver  from  its  solution  in  nitric 
acid  by  copper,  as  before  ;  to  half  an  ounce  of  this  silver,  add 
common  salt  and  muriate  of  ammoniac,  of  each  two  ounces,  and 
one  drachm  of  corrosive  sublimate  5  rub  them  together,  and 
make  them  into  a  paste  with  water.  With  this,  copper  uten- 
sils intended  to  be  silvered,  that  have  been  previously  boiled 
with  acidulous  tartarite  of  potash  and  alum,  are  to  be  rubbed  5 
after  which  they  are  to  be  made  red-hot,  and  polished. 

48.  To  prove  that  the  air  of  the   atmosphere  always  con- 
tains carbonic  acid.     This  may  be  shewn  by  simply  pouring 
any  quantity  of  barytic  water,  or  lime  water,  repeatedly  from 
one  vessel  into  another.     The  barytic  water,  when  deprived  of 
the  contact  of  air,  is  perfectly  transparent ;    but  it  instantly  be- 
comes milky,  and  a  white  precipitate,  which  is  carbonate  of  ba- 
rvtes,  is  deposited,  when  brought  into  contact  with  it  for  a  few 
minutes  only. 

The  quantity  of  carbonic  acid  contained  in  the  atmosphere, 
seldom  varies,  except  in  the  immediate  vicinity  of  places  where 
respiration  and  combustion  are  going  on  in  the  large  way,  aiul 
is  about  one  hundredth  part 


.Absorbent  vessels,  301 
Absorption  of  caloric,  35 
Acetic  acid,  198,  252 

Acetous  fermentation,  267 

acid,  252 

Acidulous    gaseous   mineral  wa- 
ters, 222 

salts,  253 

Aoids,  196 

Aeriform,  19 

Affinity,  10,  165 

Agate,  188 

Agriculture,  274 

Air,  84 

Air  pump,  53 

Albumen,  194 

Alburnum,  2C6 

Alchemists,  2 

Alcohol,  or  spirit  of  wine,  259 

Alembic,  118,  261 

Alkalies,  173 

Alkaline  earths,  174, 188 

Alloys,  155 

Alum,  or  sulphat  of  alumine,  190, 
207 

Alumine,  185,  190 

Alumium,  8 

Amalgam,  156,  182 

Ambergris,  325 

Amethyst,  191 
Amianthus,  195 

Ammonia,  or  volatile  alkali,  163, 
174,  181 

Ammoniacal  gas,  181  how  obtain- 
ed, 183 

Ammonium,  7 
Amphibious  animals,  321 
Analysis,  130 
of  vegetables,  254 

Animals,  288 

33 


Animal  acids,  199,  295 

economy,  297 

• colours,  297 

heat,  315 

oil,  243,  294 

Animalization,  140,  289,  29$ 
Antidotes,  193 
Antimony,  8 
Aphlogistic  lamp,  328 
Aqua  fortis,  21 1 

•  regia,  153 

Arrack,  261 
Argand's  Lamp,  96 
Arsenic,  8,  153,  156 
Arteries,  301,  309J 
Arterial  blood,  309,  312 
Asphaltum,  270 
Assafcetida,  247 
Assimilation,  299 
Astringent  principle,  252 
Atmosphere,  49,  84,  97 
Atmospherical  air,  85 
Attraction  of  aggregation,  or  co- 
hesion, 9,  168 

Attraction  of  composition,  11,165 
Azot,  or  nitrogen,  209 
Azotic  gas,  84 

B 

Balsams,  148 

Balloons,  112 

Bark,  283 

Barytes,  191 

Bases  of  acids,  120,  198 

gases,  85 

salts,  167 

Beer,  258  ' 

Benzole  acid,  198,  252 
Bile,  306 
Birds,  301,  321 
Bismuth ,  6 


374 


INDEX.. 


Bitumens,  270,  S27 
Black  lead,  or  plumbago,  1 37 
Bleachir/g,  204 
Blow  pipe,  132, 146 

Hare's  147 

Blood,  311,313 

Blood  vessels,  289,  311, 

Boiling  water,  55 

Bombic  acid,  295,  326 

Bones,  298 

Boracic  acid,  164,  223 

Boracium,  8,  223 

Borat  of  soda,  224 

Brandy,  261 

Brass,  155 

Bread,  268 

Bricks,  191 

Brittle  metals,  8 

Bronze,  155 

Butter,  322 

Buttermilk,  323 

c. 

Calcareous  earths,  191 

, stones,  219 

Calcium,  7 
Caloric,  17 

,  absorption  of,  35 

,  conductors  of,  36 

,  combined,  57 

,  expansive  power  of,  18,  20 

,  equilibrium  of,  26 

,  reflexion  of,  33 

— ' ,  radiation  of,  27,  31 

,  solvent  power  of,  46 

,  capacity  for,  59 

Calorimeter,  72 
Caloriuuoter,  83 
Calx,  91 
Camphor,  246 
Camphoric  acid,  198 
Caoutchouc,  248 
Carbonats,  176,  222 
Carbonat  of  ammonia,  184 

barytes,  192 

lead,  144 

lime,  193 

magnesia,  195 

— potash,  176 

Carbonated  hydrogen  gas,  136 

Carbon,  128 

Carbonic  acid,  131,  21tt 


Carburet  of  iron,  135 

Carmine,  297 

Cartilage,  300 

Castor,  326 

Cellular  membrane,  303 

Caustics,  157 

Chalk,  193,  222 

Charcoal  129 

Cheese,  325 

Chemical  attraction,  9,  166 

Chemistry,  2 

Chest,  307 

China,  190 

Chlorine,  230 

Chrome,  8,  15.3 

Chyle,  301 

Chyme,  306 

Citric  acid,  198,  252 

Circulation  of  the  blood,  30S 

Civet,  326 

Clay,  191 

Coke,  271 

Coal,  271 

Cobalt,  8,  159 

Cochineal,  297 

Cold,  26 

from  evaporation,  50,  53,  54 

Colours,  change  of,  180 

Columbium,  8,  153 

Combined  caloric,  57 

Combustion,  88 

,  volatile,  products  of, 

96 

,  fixed  products  of,  96 

,  of  alcohol,  264t, 

,  of  boracium,  224 

,  by  oxy muriatic  acid 

or  chlorine,  228 

,  of  carbon,  131,  218 

,  of  coals,  109,  137 

-,  of  charcoal  by  nitrk 


acid,  210 


-,  of  candles,  140 
-,  of  diamonds,  13 
-,  of  ether,  266 


208 


— ,  of  hydrogen,  99,  106 


-,  of  iron,  94 

,  of  metals,  145 

,  of  oils,  139 

,  of  oil  of  turpentine  br 

nitrous  acid.  167,  210 

.  of  phosphorus,  12-3 

^  of  sulphur^  1 19 


Combustion  of  potassium,  162 

,  of  candles,  108 

-Compound  bodies,  5,  173 

or  neutral  salts,  175 

Conductors  of  heat,  38,  39 

- — : , ,  solids^  36 

,  fluids,  39 

, ,  Count  Rumford's 

theory,  39 

Constituent  parts,  5 

Copper,  8,  158 

Copal,  247 

Cortical  layers,  283 

Cotyledons,  or  lobes,  279 

Cream,  322 

Cream  of  tartar,  or  tartrit  of  pot- 
ash, 353,  262 

Cryophurus,  72 

Crystallisation,  152 

Cucurbit,  117 

Culinary  heat,  42 

Curd,  322 

Cuticle,  or  epidermis,  304 


D 


Decomposition,  4 

of    atmospherical 

air,  85,  89 
—  of    water  by   the 

Voltaic  battery,  101 

of  salts  by  the  Vol- 


taic battery,  172 

—  of  water  by  metals, 


103 


136 


•by  carbon, 


224 


-  of  vegetables,  254 

-  of  potash,  164 

-  of  soda,  163  4 

-  of  ammonia,  163 

-  of  animals,  327 

-  of  the  boracic  acid, 

-  of  the  fluoric  acid, 
•olgbe  muriatic  acid, 


226 

Deflagration,  217 
Definite  proportions,  171 
Deliquescence,  207 
Detonation,  217 
Dew,  50 


Diamond,  129 
Diaphragm,  308 
Digestion,  306 
Dissolution  of  metal*,  150 
Distillation,  117,  203,  261 

of  red  wine,  261 

Divellent  forces,  170 
Division,  4 
Drying  oils,  244 
Dyeing,  249 

E 

Earths,  185 

Earthen-ware,  191 

Effervescence,  135 

Efflorescence,  206 

Elastic  fluids,  19,  85 

Electricity,  13,  74,  79,  1U 

Electric  machine,  78 

Elective  attractions,  168 

Elementary  bodies,  7 

Elixirs,  tinctures,  or  quintesceii' 

ces,  263 
Enamel,  191 
Epidermis  of  vegetables,  28 3 

of  animals,  304 
Epsom  salts,  195 
.Equilibrium  of  caloric,  26 
Essences,  245 

Essential  or  volatile  oils,  245 
Ether,  265 
Evaporation,  49 
Evergreens,  288 
Eudiometer,  125 
Expansion  of  caloric,  18 
Extractive  colouring  matter,  24.8 
Exhilarating  gas,  215 


Falling  stones,  154 
Fat,  323 
Feathers,  299 
Fecuia.  242 
Fermentation,  255 
Fibrine,  294 
Fire,  4,  14 
Fish,  320 

Fixed  air,   or  carbonic  acid,  131, 
219 

alkalies,  174 

oils,  139,  243 


376 


JtNDEX 


Fixed  products  of  combustion,  96 

Flame,  110 

Flint,  188,  191 

Flower  or  blossom,  286 

Fluoric  acid,  187,  224 

Fluorium,  or  Fluorine,  225 

Food  of  plants,  273 

Formic  acid,  295 

Fossil  wood,  271 

Frankincense,  247 

Free  or  radiant  caloric,  or  heat  of 

temperature,  27 
Freezing  mixtures,  67 

by  evaporation,  53.  72.  &c. 
Frost,  50 
Frostbearer,  72 
Fruit,  257,  286 
Fuller's  earth,  190 
Furnace,  142 


Galls,  252 

Gallat  of  iron,  208 

Gallic  acid,  208,  252 

Galvanism,  75 

Gas,  84 

Gaslights,  110 

Gaseous  oxyd  of  carbon,  134 

nitrogen,  214 
Gastric  juice,  306 
Gelatine,  or  jelly,  292 
Germination,  279 
Gin,  262 
Glands,  298,  302 
Glass,  178 
Glauber's  salts,  or  sulphat  of  soda, 

177 

Glazing  191 
Glucium,  7 
Glue,  291 
Gluten,  242 
Gold,  8,  153 
Gum,  240 

arabic,  240 

elastic,  or  caoutchouc,   248 

resins,  247 
Gunpowder,  216 
Gypsum,  or  plaister  of  Paris,  or 
sulphat  of  lime,  207 


Hall,  Sir  James,  $7 

H arrogate  water,  122 

Hartshorn,  174,  183 

Heart,  311 

Heat,  14,  18 

latent,  55,  62 
of  capacity,  58 
of  temperature,  17 

Honey,  242 

Horns,  291 

Hydro  carbonat,  110,  137 

Hydrogen,  98 

gas,  99 

I  and  J. 

Jasper,  188 

Ice,  66 

Jelly,  291,  304 

Jet,  270 

Ignes  fatui,  126 

Ignition,  56 

Imponderable  agents,  6 

Inflammable  air,  99 

Ink,  208 

Ink  spots,  253 

Integrant  parts,  5 

Iodine,  7,  235 

Iridium,  156 

Iron,  148 

Isinglass,  291 

Ivory  blacka  297 


K 


Kali,  180 
Koumiss,  324 


H 


Hair,  302 


Lac,  326 

Lactic  acid,  295,  325 
Lakes,  colours,  248 
Lamp  without  flame,  338 
Latent  heat,  55 
Lavender  water,  263 
Lead,  144,  149     * 
Leather,  250,  283 
Leaves,  281 
Life,  236 
Ligaments,  300 
Light,  14,  281 
Lightning,  210 


INbEX. 


Lime,  192 

water,  193 
Limestone,  192 
Linseed  oil,  243 
Liqueurs,  263 
Liver,  302 
Lobes,  279,  313 
Lunar  caustic,  or  nitrat  of  silver, 

157,  217 

Lungs,  310,  312 
Lymph,  301 
Lymphatic  vessels,  301 

M 

Magnesia,  195 

Magniuni,  7 

Malic  acid,  198,  252 

Malt,  258 

Malleable  metals,  8 

Manganese,  8 

Manna,  242 

Manure,  274 

Marble,  222 

Marine  acid,  or  muriatic  acid,  225 

Mastic,  247,  305 

Materials  of  animals,  289 

of  vegetables,  237 

Mercury,  8,  155 

new  mode    of  freezing, 
53,  156 

Metallic  acids,  153 
oxyds,  143 

Metals,  140 

Meteoric  stones,  154 

Mica,  195 

Milk,  302,  322 

Minerals,  142 

Mineral  waters,  134,  198 

acids,  198 
Miner's  lamp,  115 
Mixture.  47 
Molybdena,  8, 153 
Mordant,  249 
Mortar,  195 
Mucilage,  209 
Mucous^ acid,  240,  198 

membran  e,  304 

Muriatic 'acid,  or  marine  acid,  225 
Muriats,  232 

Muriat  of  ammonia,  181,  232 
lime,  67 


Muriat  of  soda,   or  common  salt, 
225,  232 

potash,  2.26 
Muriatium,  8 

Muscles  of  animals,  298,  300 
Musk,  326 
Myrrh,  247 


N 


Naptha,  160,  270 
Negative  electricity,  13,  74,  79 
Nerves,  302 

Neutral,  or  compound  salts,  196 
Nickel,  7,  154 

Nitre,  or  nitrat  of  potash,  or  salt- 
petre, 211,  216 
Nitric  acid,  209 
Nitrogen,  or  azot,  48 

gas,  90 
Nitro  muriatic  acid,    or  aqua  re- 

gia,  153,  229, 
Nitrous  acid  gas,  213 

air,   or  nitric  oxyd   gas. 
212 

Nitrats,  215 
Nitrat  of  copper,  167 

ammonia,  215,  217 
potash,  or  nitre,  or  salt- 
petre, 180,  211,  217 

silver,  or  lunar  caustic, 
217 
Nomenclature  of  acids,  120,  196 

compound    salts. 
166 

Nut-galls,  208 
Nut-oil,  244 
Nutrition  of  plants,  274 
of  animals,  298 


Oils,  138.  243 
Oil  of  amber,  271 

vitriol,  or  sulphuric  acid,  20 1      \ 
Olifiant  gas,  24t> 
Olive  oil.,  243 
Ores,  142 

Organized  bodies,  236 
Organs  of  animals,  303 
vegetables,  288 


33* 


378 


INfcEX, 


Osmium,  8,  158 
Oxalic  acid,  252, 198 
Oxyds,  150 
Oxyd  of  manganese,  145 

iron/91 

lead,  144 

sulphur,  206 
Qxydation,  or  oxygeuation,  150, 

196 
Oxygen,  7,  84,  119 

gas,  or  vital  air,  84 
Qxy -muriatic  acid,  153,  227 
Oxy-muriats,  233 
Qxy-muriat  of  potash,  233 


Palladium,  153 
Papin's  digester,  292 
Parenchyma,  279,  283 
Particles,  9 
'Pearl-ash,  176 
Peat,  271 

Peculiar  juice  of  plants,  283 
Perfect  metals,  8 
Perfumes,  245 
Perspiration,  314 
Petrifaction,  270 
Pewter,  155 
Pharmacy,  2 
Phosphat  of  lime,  209 
Phosphorated  hydrogen  gas.  126 
Phosphorescence,  16 
Phosphoric  acid,  208 
Phosphorous  acid,  208 
Phosphorus,  123 
Phosphoret  of  lime,  126 

sulphur,  127 
Pitch,  283 
Plaister,  195 
Platina,  8,  147 
Plating,  155 
Plumbago,  139 
Plumula,  279 
Porcelain,  191 

Positive  electricity,  13, 74, 79,  &c. 
Potassium,  8,  160,  162 
Pottery  190 
Potash,  160 
Precipitate,  12 

Pressure  of  the  atmosphere,  55,  56 
prussiat  of  iron,  or  Prussian  blue, 
295 


Prussiat  of  potash,  295 
Prussic  acid,  295 
Putrid  fermentation,  268,  326 
Pyrites,  155,  207 
Pyrometer,  20,  25 

Q 

Quicklime,  192 
Quiescent  forces,  170 

R 

Radiation  of  caloric,  28 

Prevost's  theory,  27, 

Pictet's    explana- 
tions, 28 

Leslie's  illustrations, 
31 

Radicals,  196,  199 

Radicle,  or  root,  279 

Rain,  50 

Rancidity,  245 

Rectification,  262 

Reflexion  of  caloric,  28,  31 

Reptiles,  321 

Resins,  246 

Respiration,  307 

Reviving  of  inetals,  147 

Rickets,  299 

Rhodium,  153 

Roasting  metals,  142 

Rock  crystal,  188 

Ruby,  187 

Rum,  261 

Rust,  143,  148 


Saccharine  fermentation,  256 

Sal  ammoniac,  or  muriat  of  ainfliQ- 
nia,  181 

polychrest,  or  sulphat  of  pot- 
ash, 205 

volatile,  or  carbonat  of  am> 
monia,  184 

Salifiable  bases,  167 

Salifying  principles,  167 

Saltpetre,   or  nitre,    or  nitrat  ol 
potash,  180,  211,  217 


INDEX. 


379 


Salt,  150,  205 

Sand,  189 

Sandstone,  189 

Sap  of  plants,  239,  257,  286 

Sapphire,  187 

Saturation,  48 

Seas,  temperature  of,  41 

Sebacic  acid,  245,  195 

Secretions,  313 

Seeds  of  plants,  257,  286 

Seltzer  water,  134,  194 

Senses,  303 

Silex,  or  silica,  185,  188 

Silicium,  8 

Silk,  326 

Silver,  145 

Simple  bodies,  5 

Size,  291 

Skin,  290 

Slaking  of  lime,  192,  303 

Slate,  190 

Smelting  metals,  142 

Smoke,  96 

Soap,  176 

Soda,  163,   180 

water,  136 
Sodium,  163 
Soils,  273 
Soldering,  155 
Solubility,  205 
Solution,  46 

by  the  air,  47 
of  potash,  178 
Specific  heat,  59 
Spermaceti,  325,  327 
Spirits,  260 
Spirit  lamp,  264 
Steam,  57,  65 
Steel,  138 
Stomach,  306 
Stones,  186 
Stucco,  195 
Strontites,  195 
Strontium,  8 
Suberic  acid,  252,  198 
Sublimation,  117 
Succin,  or  yellow  amber,  271 
Succinic  acid,  252,  271 
Sugar,  240,  256 

of  milk,  324 
Sulphats,  197 

Super-oxygenated  sulphuric  acid, 
196 


Sulphat  of  alumine,  or  alum,  190 
barytes,  192 
iron,  207 

lime,    or    gypsum    or 
plaister  of  Paris,  207 

magnesia,    or    Epsom 
salt,  195,  207 

potash,    or  sal    poly- 
chrest,  205 

soda,orGlauber's  salts, 
177,,  206 
Sulphur,  117 

flowers  of,  117 

Sulphurated  hydrogen  gas,  122 
Sulphurets,  155 
Sulphurous  acid,  203 
•Sulphuric  acid,  201 
•Sympathetic  ink,  159 
/Synthesis,  130 

T 

Tan,  249 

Tannin,  251 

Tar,  283 

Tartarous  acid,  252 

Tartrit  of  potash,  253 

Teeth,  298 

Tellurium,  8 

Temperature,  17 

Thaw,  73 

Thermometers,  21 

Fahrenheit,  21 
Reaumur's,  22 
Centrigrade,  22 
air,  22 

differential,  23 
construction  of,  23 

Thoracic  duct,  301 

Thunder,  113 

Tin,  145,  159 

Titanium,  156 

Turf,  271 

Turpentine,  167,  283 

Transpiration  of  plants,  280 

Tungsten,  8, 153 


Vapour,  57,  65,  266 
Vaporisation,  49 
Varnishes,  247 
Vegetables,  236,  272 
Vegetable  acid,  188,  252 


380 


INDEX- 


Vegetable  colour?,  248 
heat,  2:37 
oils,  244 
Veins,  304,  309 
Venous  blood,  309,  312 
Ventricles,  310 
Verdigris,  158 
Vessels,  301 
Vinegar.  267 
Vinous  fermentation,  258 
Vital  air,  or  oxygen  gas,  84 
Vitriol,  or  sulphatof  iron,  201 
Volatile  oils,  139,242,  245 

products   of  combustion. 
254 

alkali,  174, 181 

Voltaic  battery,   142,    146,    160, 
172 


Uranium,  8 


u 


w 


Water,  99,  107 

decomposition  by  carbon, 
136 


Water,  decomposition  of,  by  elec- 
tricity, 107,  &c. 

condensation  of,  41 

of  the  sea,  41 

boiling,  45,  55 

solution  by,  47 

of  crystallisation,  152 
Wax,  244,  325 
Whey,  322 
Wine,  258 
Wood,  200 

Woody  fibre,  251,  SJ84 
Wool,  299 


Yeast,  267 
Yttria,  185 
Yttrium,  7 


Zinc,  8 
-Zicornia,  185 
Zoonic  acid,  295 


TABLE  OF  THE  EFFECTS  OF 


Fahrenheit. 

—  55 

46 

39 

36 

22 

11 

7 


20 


25 

28 
30 
32 

36 
46 

$4 


40 

82 
97 
90 
104 
109 
112 
127 
149 
145 
155 
212 


1.    FREEZING   POINTS    OP   LIQUIDS. 


Strongest  nitric  acid  freezes  (Cavendis.1)) 

Ether  and  liquid  ammonia 

Mercury 

Sulphuric  acid  (Thompson) 

Acetous  acid 

2  Alcohol,  1  water 

Brandy 

Strongest  sulphuric  acid  (Cavendish) 

Oil  of  turpentine  (Macquer) 

Strong  wines 

Fluoric  acid 

Oils  bergamot  and  cinnamon 

Human  blood 

Vinegar 

Milk 

Oxymuriatic  acid 

Water 

Olive  oil 

•Sulphuric  acid,  specific  gravity  1JTS  (Keir) 

Oil  of  anniseeds,  50  (Thompson} 

2.    MELTING  POINTS  OP  SOLIDS. 

Equal  parts  of  sulphur  and  phosphorus 

Adipocire  of  muscle 

Lard  (Nicholson) 

Phosphorus 

Resin  of  bile 

Myrtle  wax  (Cadet) 

Spermaceti  (Bostock) 

Tallow  (Nicholson)  92  (Thompson) 

Bees'  wox 

Ambergris  (La  grange) 

Bleached  wax  (Nicholson) 

Bismuth  5  parts,  tin  3,  lead  2 


382 


TABLE    OF    THE 


Fahren. 

Wedg. 

234 

235 

383 

303 

-334 

442 

460 

476 

612 

680 

809 

3809 

21 

4587 

27 

4717 

22 

5237 

32 

17977 

130 

20577 

150 

21097 

154 

21637 

158 

21877 

160 

23177 

4-170 

140 

145 

170 

176 

212 

219 

230 

242 

248 

283 

540 

554 

560 

570 

590 

600 

660 

Sulphur  (Hope)  212  (Fourc.)  185  (Kirw.) 
Adipocire  of  biliary  calculi  (Fourcroy) 
Tin  and  bismuth,  equal  parts 
Camphor 

Tin  3,  lead  2,  or  tin  2,  bismuth  1 
Tin  (Chrichton)  413  (Irvine) 
Tin  1,  lead  4 
Bismuth  (Irvine) 

Lead  (Crichton)  594  (Iry.)  540  (Newton) 
Zinc 

Antimony 
Brass 
Copper 
Silver 
Gold 
Cobalt 
Nickel 
Soft  nails 
Iron 

Manganese 

Platinum,  tungsten,  molybdena,  uranium,  ti- 
tanium, &c. 

3.    SOLIDS  AND  LIQUIDS  VOLATILIZE®. 

Ether  boils 
Liquid  ammonia  boils 
Camphor  sublimes  (Venturi) 
Sulphur  evaporates  (Kirwan) 
Alcohol  boils,  174  (Black) 
Water  and  essential  oils  boil 
Phosphoius  distils  (Pelletier) 
Muriate  of  lime  boils  (Dalton) 
Nitrous  acid  boils 
Nitric  acid  boils 
White  arsenic  sublimes 
Metallic  arsenic  sublimes 
Phosphorus  boils 

Oil  of  turpentine  boils,  about  212°  (Dalton) 
Sulphur  boils 

Sulphuric  acid  boils  (Dalton)  546  (Black) 
Linseed  oil  botls,  sulphur  sublimes  (Davy) 
Mercury  boils  (Dalton)  644  (Secondat)  600 
(Black)  672  (Irvine) 


EFFECTS    OF    HEAT. 


383 


4.    MISCELLANEOUS  EFFECTS  OF  HEAT. 


Wedg. 


1 

f-  2 

6 

14 

40 

57 

70 

86 

94 

102 

105 

H2 

114 

121 

124 

125 

150 

185 


Greatest  cold  produced  by  Mr.  Walker 

Natural  cold  produced  at  Hudson's  Bay 

Observed  on  the  surface  of  the  snow  at  Glas- 
gow, 1780 

At  Glasgow,  1780 

Equal  parts,  snow  and  satt 

Phosphorus  burns  slowly 

Vinous  fermentation  begins 

to  135  Animal  putrefaction 

to  80  Summer  heat  in  this  climate 

Vinous  fermentation  rapid,  acetous  begins 

Phosphorus  burns  in  Oxygen,  104  (Gottling) 

Acetification  ceases 

to  100  Animal  temperature 

Feverish  heat 

Phosphorus  burns  vividly  (Fourcroy)  148 
(Thomson) 

Albumen  coagulates,  156  (Black) 

Sulphur  burns  slowly 

Lowest  heat  of  ignition  of  iron  in  the  dark 

Hydrogen  burns,  1000  (Thomson) 

Charcoal  burns  (Thomson) 

Iron  red  in  twilight 

Iron  red  in  day  light 

Azotic  gas  burns 

Enamel  colours  burned 

Diamond  burns  (M'Kenzie)  30  W.  =  5000 
F  (Morveau) 

Delft  ware  fired 

Working  heat  of  plate  glass 

Flint  glass  furnace 

Cream-coloured  ware  fired 

Worcester  china  vitrified 

Stone  ware  fired 

Chelsea  china  fired 

Derby  china  fired 

Flint  glass  furnace  greatest  heat 

Bow  china  vitrified 

Plate  glass  greatest  heat 

Smith's  forge 

Hessian  crucible  fused 

Greatest  heat  observed 


Y6  36017 


M289981 


THE  UNIVERSITY  OF  CALIFORNIA  UBRARY 


